As they crossed the Great Plains of America, Harry was certain she’d never seen anything so astonishing in all her life.

The Kestrel hadn’t had such a long stretch airborne since she crossed the Atlantic. Even on the third day of it, Harry leaned out a window to watch the land passing beneath them, and what seemed to be all of heaven passing above. “Have you ever seen the sky look so very large, Marlowe?”

“Only at twenty thousand feet of altitude.”

Twenty thousand was nearly the upper limit of military-grade airship capabilities. Any higher, the air ran out. The sky was huge at altitude, but very lonely. According to the barometric altimeter, they were at some five thousand feet altitude now—only two thousand, vertical: Details of the ground spread out as on a map. Wind buffeted them, the sun blazed down. They might have been flying over an ocean, but this was grass, hundreds of miles of it, rippling with shadows and light. The yellowing plain seemed barren, featureless and undisturbed. Easy to become disoriented, when all directions looked the same.

The plains weren’t really so desolate—at regular intervals, small towns grew up like weeds along the rail line. About a day’s wagon trip apart, each of them. The Kestrel wouldn’t be lost, if something happened out here. Harry was almost sad about it—she didn’t really mind the loneliness of being in an airship over an endless plain.

She had to search for it, but she picked out the double lines of the railroad tracks, along with accompanying telegraph wires on posts, that guided them on. Best way to navigate in such a place. Someone might have taken a pencil to a map. She followed the line west, where something like a mirage disturbed the sameness of the planes, a rough gray splotch, rising like some distant wall.

“Marlowe, you’ll want to look at this,” she said, nodding ahead.

A smile flickered on his lips as he made another small course correction, heading directly toward that gray shadow.

The Rocky Mountains.

• • • •

They stopped briefly in Colorado Springs, an oasis on the plains that was very nearly cosmopolitan. Pikes Peak rose like a tower to the west of the town, some fourteen thousand feet in altitude. The mountains were a wall marking the end of the plains, and they kept going, peak after peak. Traversing them in the airship would be a challenge.

They’d had a bit of a scare approaching the town. Marlowe squinted some distance south, and Harry took up the spyglass. Another airship, even smaller than the Kestrel, with an open gondola, traveled at an easy pace. Three men were on board.

“They’re flying a U.S. Cavalry flag, I think,” she said. “A local patrol, perhaps? That ship certainly isn’t built for distance.”

“I’d wondered if the cavalry would use airships out here. Best way to keep track of all this territory, I should think.”

Sun glinted off the other gondola, a reflective flash. A man looking back at her through his own spyglass. “They’re watching us,” she said.

“Run up flags. I don’t want to waste time explaining ourselves to them.”

Naval semaphore flags worked just as well inland, and Harry raised the flags along their gondola that identified them as a private ship registered in Chicago. A lie, of course, but nothing would draw the attention of the U.S. Cavalry faster than if she raised the correct British Navy flags. Fortunately, the patrol vessel believed them and maintained its course north and east.

The Kestrel had drawn attention wherever she flew in America. Harry found herself avoiding the crowds as much as she could—a stray photograph of her placed in front of knowing eyes might reveal her true identity, and that wouldn’t do at all. Her and Marlowe’s roles here were part tourists, part spies, and part archeologists. Marlowe put himself forward as a research assistant to a member of the Royal Academy, gathering notes for a treatise on Aetherian technology outside of Britain. To preclude awkward questions, Harry was usually introduced as a relative of his along for the education. No one knew that she was also Princess Maud of Wales, and she hoped that if by some strange chance they met someone who recognized her, such a person would have the good sense to keep quiet about it.

They were searching for innovation. For something new. As was their wont, the Americans had taken Aetherian technology like locomotive engines and made them faster, cheaper, and more efficient. They had adapted the Aetherian engines to the paddlewheel ships that plied the Mississippi. They had also done things like build an entirely mechanical elephant, billed as Jumbo from the Stars, which currently performed in a specially built arena at a place called Coney Island.

So far, though, she and Marlowe had found nothing new, and no evidence that anyone had stumbled upon lost artifacts not part of the original Aetherian wreckage at Surrey.

In Colorado Springs, they obtained a set of local maps and identified their next destination: a small crossroads town in the mountains called Alamosa.

“Remind me: How did you discover this place?” Marlowe asked. He had the new maps spread out on the collapsible table set up in the middle of the cabin. Colorado Springs had a number of hotels that were meant to be very fine, and Harry thought longingly of a hot bath and a dinner on fine china. But they hadn’t indulged in New York, Baltimore, or even St. Louis, and they most certainly wouldn’t indulge here. They were on campaign, as she thought of it. Better to maintain their cover as academics of only moderate means. When needed, a curtain divided the cabin into two makeshift rooms, and Marlowe was a model of propriety. On the other hand, she was an only partially successful aspirant toward propriety.

“A dime novel, would you believe?” she said. “‘The True Story of the Haunted Locomotive of the Rockies.’ I’ve got a copy stashed in my trunk if you’d like to see it.”

“Are the illustrations very lurid? Then I might.”

She dug in her trunk, stowed under one of the benches, and found the book, which indeed had an astonishing engraving on the cover: a locomotive with flames streaming from its coupling rods and a cattle guard in front stretching open like a fang-filled mouth.

Marlowe regarded the picture skeptically. “Are you telling me you’ve planned the next stage of this expedition based entirely on a story in a penny dreadful?”

That wouldn’t have been the worst reason she’d offered for an expedition. “Not entirely. I also found some newspaper stories of accidents and strange goings-on, all involving this one stretch of rail out of this one town.” She presented a newsprint clipping tucked into the pages of the book.

Marlowe read aloud. “‘Three experienced engineers vanished into thin air after attempting to travel with the engine. Since then, no others have dared attempt the journey. The phantom train departs on schedule and returns on schedule . . . without any human guidance. The metal of the steel monster glows green in the dark.’ Ah, I see.”

She said, “I think someone made some improvised modification to an Aetherian engine and created something entirely new. Or perhaps someone has discovered some new artifact, some remains from an undiscovered Aetherian landing.”

“Or it could all be a sensationalist tale from a dime novel.”

“It could, but it’s worth a look. And the stationmaster in Alamosa is offering a bounty for anyone who can disable the engine and stop the train. Four men have already vanished in the attempt—presumed dead, devoured by the monster engine. This is in addition to the three missing engineers.”

“Good God, how can I turn down a challenge like that?”

She grinned. “I thought you’d say that.”

• • • •

They reached Alamosa in a few hours of moderate flying the next day—the winds in the mountains were unpredictable, and Marlowe stayed alert at the helm. By then, Harry had to admit that any romantic notions she’d harbored about the American West were terribly outdated. Like Colorado Springs, Alamosa was a respectable town, with wide main streets and brick and stone buildings, modern construction and plentiful telegraph poles. No stagecoaches in sight, no stampedes, no shootouts between marshals and bandits. Indians, identifiable from their shining black hair and brown skin, wore the same clothes as other citizens of the town: dungarees and button-up shirts. A Chinese-operated laundry had a glowing, Aetherian-powered water heater and steamer in its back alley. Marlowe might want to have a look at the improvisations that had been made to it. This was just a town, like any other. The haunted locomotive was probably also all legend.

For all its modernity, the town did not have an aerial mooring. “It’s the mountains, I imagine,” Marlowe explained. “The winds are so intractable, trains are simply a more reliable form of transportation.” He was clearly cross from fighting to keep the Kestrel level.

“Except when they’re taken over by Aetherian ghosts,” Harry said.

“Well, yes. What they really need out here are some German pilots to train them—all that practice flying over the Alps. Not that I’m going to suggest it.”

Marlowe found an open lot outside of town where he could lower the Kestrel by partially deflating its bladder. They would not set down, but they could use a rope ladder to descend and anchor the ship via stakes in the ground. Marlowe climbed down with a bundle of long metal stakes and a hammer, while Harry threw him lines to tether the gondola.

A crowd had gathered to watch. People kept a respectable distance, shading their eyes to stare up at the balloon and the Aetherian motor, which, even powered down, gave off a hum and a glow.

A man detached himself and stepped forward, hesitant—perhaps because of the large hammer Marlowe was swinging. Time for Harry to intervene.

She wore a long divided riding skirt, a blouse and vest, good boots and gloves. Her hair was pinned up under a brimmed hat. Not her preferred ensemble for real work, but she’d had a feeling she’d need to look respectable while talking to nervous officials. She wondered if this man wore a brass star under his suit coat, or if that was another outdated romantic notion.

“Hello, there!” she called to him, climbing down the ladder, satchel over her shoulder. “I do hope it’s acceptable that we moor here for a day or two. We’ll pay a fee—rent for the land, if you like. We’ve got to purchase some supplies, and have some other tasks as well. My name is Miss Mills.”

She stuck out her hand for shaking, giving him no chance to refuse. The man seemed just as startled by her as by Marlowe and the hammer, either because of her English accent, her forward manner, or both. But he’d brightened at the mention of money, as she’d hoped he would.

He was an older man with greying hair, but still fit of form. “Conrad Finch, ma’am. I’m the deputy mayor here. I gotta say, we don’t often see airships at all, much less such fine . . . foreign . . . ones as this. With the war on in Europe, I’d have thought a ship like this would be in the fighting.”

The man had a good eye—American ships tended to have open gondolas, unlike the solid closed gondola of the Kestrel, and Finch had probably never seen anything so modern as her very fine engine. She wondered how much he was really asking: Were they deserters? Had they stolen this ship from the Navy? Were they spies on some mission, or something else entirely? To a knowing eye, the Kestrel was certainly a military-grade vessel, for all that they’d disguised her with clumsy bags of ballast and unpolished brass fittings.

Harry entirely ignored the implied questions. “Pleasure to meet you, Mr. Finch. May I introduce James Marlowe, the pilot of the Kestrel?”

Marlowe let the hammer hang at his side as he finally came over to meet the locals. Watching the crowd, Harry saw him through their eyes: he looked exactly like an airship pilot should, with a leather jacket and scarf, tall boots, goggles pulled down around his neck, and a windburned glow to his stubbled face. As romantic as any heroic archetype the American West had produced. She sighed a little.

“I suppose you’re wondering why we’ve come out all this way,” Marlowe said.

“Well, I suppose so. Like I said, we don’t get airships out here too often. What with the mountains and all.” He gestured over his shoulder. From here, the mountains seemed a long way off. Alamosa was in a valley—the mountains were a barrier surrounding them.

“We’d like to have a look at that phantom locomotive of yours,” Marlowe said, smiling a perfectly agreeable, innocent smile.

Finch’s expression fell. If Harry had to name the distant look that had entered his gaze, she would have called it haunted. He spoke in the tone of someone announcing a death.

“You’ll want to talk to Cooper.”

• • • •

They determined ownership of the lot, negotiated and paid a reasonable fee, and even found a pair of trustworthy men to hire as guards. In fact, a handful of them argued for the honor, and Harry got a very good rate for their time.

Then it was off to see this train.

The train yard was bustling, with several different lines running through town and branching off. A chalkboard timetable hung in a waiting area, which was clean and inoffensive, if not terribly comfortable.

Outside, only two of the five locomotives parked or traversing the yard had been adapted to run on Aetherian engines, and the modifications were entirely standard, nothing usual or noteworthy about them. Nothing growling or monstrous, as on the lurid engraving.

Finch found the stationmaster in an office toward the back, where a large window overlooked the yard. The office door stood open, and the trio of them, trailed by a few onlookers and other officials who’d not stayed behind to gawk at the Kestrel, trooped up to the threshold. The deputy mayor knocked on the doorframe.

“Cooper? These folks are here to try for the ghost,” he said curtly, a sour look on his face.

A heavyset and overworked-looking man looked up from the cluttered desk where he sat, and with a sigh he stood and put on his suit jacket, which had been hanging over the back of his chair. His gaze fell on Harry, and an eyebrow raised in curiosity. Finch made introductions. The stationmaster was simply Mr. Cooper, and as expected, he directed his statements at Marlowe. His expression was grim, his frown pulling down his sideburns. “Son, a dozen men before you have come here thinking they can tame that monster, and every one of ’em is dead. What makes you any different?”

“I’m British,” Marlowe said, a wicked twinkle in his eye, giving Harry a sideways glance. “And I have the able assistance of Miss Mills.”

Cooper looked them up and down, and seemed on the verge of countering the challenge. He only shook his head. “Ma’am, with all due respect, you do not want to get involved with this thing.”

“Oh, I think I do,” she said calmly, not inviting argument.

Marlowe said, “I was hoping you could give us some more information beyond what’s in the newspapers and penny dreadfuls.”

Both Cooper and Finch shook their heads at that. “Damn that reporter—pardon me, ma’am—who came through. That book is going to be the only thing anyone remembers about Alamosa.”

“When did the trouble start?”

Cooper sat heavily, and the others took up comfortable positions leaning on walls, arms crossed or hands in trouser pockets.

“Six months ago. Before that everything was fine, just fine. This train—it makes a run over the pass to Gunnison and back. It’s a local line, once a day, shouldn’t be trouble. But one day the regular engine broke down, and we had one of the bug-rigged ones hanging around—”

“Bug-rigged?” Harry asked.

“Aetherian-adapted, I think,” Marlowe said.

She had never heard the term before. It was amusing, appalling, and appropriate, all at once. God bless the Americans and their ornamental figures of speech. “Go on,” she said.

“We hitched it on up to the regular train, mostly freight and a couple of Pullman cars. Five hours later, I get a telegram from the Gunnison station wanting to know where the train is. Couple hours after that is when the train rolls back here. A dozen passengers stormed off, the driver was white as a ghost, but no one could say what happened. The thing got up into the mountains, into one of the tunnels, everything went dark, there was a bunch of noise, and when it came back out of the tunnel, it was . . . different. It’s got, well, some kind of stuff on it.” That haunted look again.

“I sent the train back on schedule the next day with another driver and a couple of guards. The train came back on schedule that afternoon. They didn’t. No sign of trouble, it’s like they just hopped off the train and sent it rolling back here. We haven’t gotten anything through that line in six months. We’re having to reroute through Durango.”

“And the company’s done nothing to investigate?” Marlowe asked.

“Sure they have. Sent people up on horseback, checked the tracks, checked the tunnel. Watched the train—it stops in the tunnel and turns right back around, all by itself. Whenever we put a driver on it—the driver don’t leave the tunnel. Can’t get anyone to try again. So now we’ve got the bounty. You figure out what’s happening up there, the railroad’ll pay ten thousand dollars. But I’m not putting any bets on you.”

Finch said, “Man with an airship like yours don’t need ten grand, I expect.”

“It’s true. We’re not here for the reward,” Marlowe said. “We’re here for the adventure.”

“Then you’re even crazier than I thought,” Finch huffed. “Both of you.”

Cooper pointed at Harry. “You’re not getting the lady involved, are you? You’re not taking her up the mountain?”

“Why wouldn’t I go?” Harry said.

The stationmaster flustered. “Well. It’s just. I—it’s dangerous, ma’am. We’ve got a fine hotel here in town if you want to wait for your . . .” The word husband was on the tip of his tongue, until he evidently remembered their different last names. He didn’t know what she was.

“I make my own choices, Mr. Cooper,” she said.

“Train pulls in every day at noon. You want to take a shot, I won’t stop you. It’s never late. Wish all my trains kept their schedules like that.”

“We won’t be held responsible for anything that happens to you,” Finch said. “’Round here, we’re used to folks heading into the mountains to prospect or whatnot, and never coming back. You won’t get special notice.”

Harry hid a smile, because they didn’t know she was a princess of England, and if she vanished, someone would certainly give her special notice. “We understand. Thank you.”

• • • •

Marlowe had that enviable Naval ability to claim sleep in the space of minutes, in any position, in any environment. He stretched out on the padded bench in the Kestrel’s main cabin, and that was that. Harry tried to do the same in the pilot’s chair, and failed. Their plan was in place—as much of a plan as they could make until they got their first look at the locomotive. Then they would board a machine that had evidently killed a number of men and made their bodies vanish.

She tried to imagine what they might see in that moment, but failed to conjure a picture.

“Harry,” the lieutenant mumbled. “Try to sleep.”

“Yes, I know,” she sighed.

“There’s nothing we can do until morning. You need to rest.”

“Yes.”

“There’s a flask in the pouch behind the pilot’s chair.”

“I know where the flask is, Marlowe.” A swallow of whiskey would, in theory, put her a step or three closer to sleep.

“Well then. You know your mind.” A moment later, he was snoring softly.

Digging in the pouch hanging over the back of the chair, she found the metal flask and took the swallow. The drink warmed her, but it was still another hour before she got any sleep at all.

• • • •

Harry wore trousers the next day, propriety be damned. Today, she had to be ready to move. Her boots were scuffed, her gloves worn, her jacket weather-stained. Anyone could see this was not her first time out in the world.

On the ground under the Kestrel, she secured her pistol in its holster at her hip. It was an Aetherian pistol, the kind Britain didn’t export. It would be as rare a sight here as the Kestrel, but with luck no one would notice she had it. After she pulled her pack and coils of rope over her shoulder, she looked up at the ship and said a silent farewell.

“We’ll solve this,” Marlowe said, coming up by her shoulder with his own gear, instruments and tools slung in pouches on a bandolier and belt. “We’ll be back at noon tomorrow.”

“Yes,” she said. “I know.”

On the way out, Marlowe talked to their impromptu guards. “Do resist laying claim to her until you’re sure we’ve failed to return on the noon train tomorrow, yes?”

The two men stammered and scuffed their toes, but they agreed to keep watch at least until then.

Cooper was waiting for them on the platform outside the station, pocket watch in hand. So was Finch, along with a crowd of townsfolk come to see them off. Gawkers. Harry might have wished for less publicity. They had five minutes until the phantom locomotive arrived.

“I feel like we’re heading out to harpoon a whale,” she murmured.

“Surely this won’t be anything so dramatic. We take a look at the thing, board it if necessary, see where it takes us while examining and disabling the machinery. The men who’ve tried this before had little experience with Aetherian machinery. It’s been waiting for us to come and speak to it in its own language.”

“I do hope that was a metaphor.”

“Here it comes,” Cooper said, looking out along the tracks to the north. “Right on time.”

No shrill, distant whistle announced the engine’s approach. Only the clank of wheels against rail and the low, throbbing hum of an Aetherian drive emitting a great deal of power. The townsfolk who were present backed up, pressed themselves to the wall of the station as the beast slowed and came to a stop at the platform. It moved in reverse on this leg of the journey, pushing its coal car ahead of it. As Cooper had explained, the rest of the cars had been uncoupled, so only the engine and former coal car remained, a monstrous beast plying the tracks with a will of its own.

It didn’t look like a steam locomotive fitted with an Aetherian drive, or even one designed with Aetherian technology from the first. This was something else entirely, and wholly unlike any machine Harry had seen. In an adapted locomotive, the Aetherian generator was typically built into the furnace, with tubes and pistons connecting the generator to the side rods along the engine’s wheels. But while this engine might once have been a retrofitted steam locomotive, it had changed: Where the tubes and pistons connected the side rods along the wheels to the Aetherian generator, typically built into the firebox in such an arrangement, additional cabling looping around the broiler and into the cabin, growing almost organically in the manner of vines, obscuring the windows, stretching over the roof and reaching back. Wires tangled around each other over the coupler, swarming to the empty coal car, where the tips of the tendrils lay reaching out along the metal, waiting to extend further. All of it glowed a pale green, the familiar sickly, pulsing light that seemed to accompany all things Aetherian.

“Bug-rigged, indeed,” Harry said.

“I’ve never seen anything like it,” Marlowe breathed.

That gave Harry pause. She’d never heard Marlowe hesitate over anything, particularly where research was concerned. She had seen many of the same extreme Aetherian experiments he had. But this—was something else. “Marlowe, if you aren’t sure—”

“No. Let’s go. We’ll alight on the coal car.” The back half of the car remained free of Aetherian growths; the steel box seemed safe enough. Marlowe was still looking at the engine—something had caught his attention.

Stationmaster Cooper said, “You folks only have a minute to get on. If you’re sure you want to do this.”

“Thank you,” Harry said. “We’ll see you tomorrow then, yes?” Cooper just shook his head.

Harry and Marlowe kept hold of their ropes and wrenches, wire cutters and all the rest, and hopped on to the ledge at the end of the coal car just as the engine hummed to a higher pitch, reversed direction, and clacked back along the tracks, away from the station and toward the mountains.

• • • •

She had the feeling they had grabbed the tiger by the tail.

They settled on the narrow platform at the back of the coal car, keeping hold of a railing there, while the engine slipped through the yard and out of town. It ran smoothly, its hum almost out of hearing; all she heard was the rhythmic clanking of wheel on track. But the machinery before her was like the gaping maw of some fantastical creature.

Tubing and glowing wires looped out from the cab across the coupling to the coal car—the tender. The ends trailed off, fused to the steel sides. The tender itself was empty—unnecessary, once the engine had been converted. Inside, the cab was filled with twisted mechanisms that seem to have grown rather than been built. The controls and levers had been obscured, only visible if you knew where to look. The door to the furnace was open, and the green of the Aetherian generator inside pulsed. Nothing came out of the chimney but an occasional green spark. As Cooper and Finch had said, there was no sign of a driver, an engineer, or anyone else. The thing was entirely autonomous.

Marlowe used his spyglass to study components of the engine. “I think—I believe much of the mechanism has grown from the original alterations. It’s not unheard of; some wiring from the Surrey crash seemed to have plant-like properties. Some samples kept sealed in a box were discovered years later to have grown. Nothing like this.” He leaned out, keeping one hand on the railing, for a better look at the outside. “There—that’s the standard retrofit. Everything else was added, and not by any known principles of Aetherian mechanics.”

“So we’re dealing with unknown principles. Is there some mad scientist in the hills making alterations, then sending the thing back? Murdering those who try to stop him?”

“An American mad scientist would be trying to patent the thing, I expect,” he said.

“Then what if someone found a cache of Aetherian artifacts of unknown properties, introduced them to this engine, and got far more than they expected?”

He nodded. “If some prospector found a previously unknown Aetherian crash site in these mountains—well, anything could happen.”

They were outside the town now, and the locomotive seemed to accelerate. They still had time to jump without being seriously injured. Soon they would reach the hills and mountains beyond. The sky overhead was searing blue. With no choking coal smoke pouring from the engine, she could smell fresh, chill air from the mountains.

Marlowe continued. “I expect what we’ll find is some camp in the mountains. Someone’s altered the engine with some new artifact they found, but they can’t shut it down, and so it keeps running this route via some kind of automatic instructions built into this new wiring. When someone rides the train up, they’re taken prisoner, and there you have your haunted locomotive.”

“So what will we do when we get there, reason with them?”

“That’s your job,” he said archly. “For my part, I think I can disable the engine, just as soon as I find the nonstandard component. Remove it, see what makes it tick, get the thing back under control. I imagine our amateur engineer will be grateful.”

They studied the weird mechanics grown in and around the cab, searching for that nonstandard component, that thing that didn’t look familiar or right. Really, the entire locomotive was unfamiliar and wrong, so trying to find just one aberration was difficult. In fact, the more she looked, the more wrong it looked. Not just unsettling—no matter how much she and her world depended on Aetherian machinery, she’d always felt some discomfort around the more extreme examples—but deeply wrong.

Finally, Marlowe said, “I think . . . ah yes, that’s new. There’s a touch of red in the firebox. I thought it was overheated metal, but I think it’s an independent source of radiation.”

“Marlowe, let me see that a moment.” She held her hand out, and he gave her the spyglass.

Stretching up, anchoring against the railing at the back of the tender, she looked through it, not at the mechanical parts of the engine, the glowing of the firebox—she saw the spot of red Marlowe mentioned, like a candle in a fogbank—and adjustments made to the valves and rods. She focused on the shadows inside the cab, on vague details hidden there.

A bit of red fabric, like from a kerchief worn about the neck, fluttered in a corner. A few feet beyond it, a tuft of brown hair sprouted from a pressure gauge. Near the roof was a hand, colored green as if grown over with moss, pierced through with glowing Aetherian wires.

Harry lowered the spyglass and settled on the platform. “Marlowe, I think we’ve got to get off this thing.”

“Do you know how fast we’re going?”

She spared a glance; the valley’s grassy meadow slipped by in a blur. Trees of the forest ahead were now visible. They could no longer leave the train without being smashed on the ground.

She said, “Look in the cab, at the roof above the gauges.”

He took the spyglass, and she pointed out the details she’d found, the odd human scraps among the alien whole.

“We’ve got to slow down at some point,” he said.

“Yes, and we’ve got to stop the thing,” she answered. “Before it kills us.”

What had started as a treasure hunt, a search for new and unknown Aetherian artifacts to advance British supremacy, had become a bit more serious.

“We’re already ahead of the game,” he said. “The others—the unfortunate drivers, the bounty hunters who boarded later—all entered by the cabin. They thought to control the train from there. It would have been intuitive. We’ve come at it roundabout. That gives us a little time, yes?”

Marlowe moved inside the coal car, braced up against the wall to shelter from the wind now whipping past the speeding train. Searching through the pouches slung over his shoulder, he gathered bits and pieces, wires and clamps. He obviously had a plan.

The air was growing cold. The train had entered a wooded stretch, and the mountains now rose up around them. Still, they were accelerating. How the train could navigate the mountain tracks at this speed, she didn’t know.

He put a pair of needle-nosed pliers in his mouth while he fished for another piece out of a pouch. He was building something, right there amidst the rocking and shaking of the train. It had a lot of spiky bits and some kind of filament in the center that looked flammable.

“What exactly is it you’re making?”

“A bypass . . . I think. To bleed off some of that power it’s using.”

They were roaring through the forest, moving faster than metal wheels on a metal track ought to be able to move. The trees passed by in a blur.

“Done,” Marlowe said, shoving tools back into pouches and pulling himself to his feet. He held an object about the size of an apple, vaguely spider-shaped, with wires sticking out as legs, barbs at the tips looking like weapons. The body of it was a collection of loops and circuits and diodes. A filament glowed green with incipient power. “A bit of a prayer may be in order.”

He then threw the device before Harry had time to make that prayer.

It sailed straight and true into the cab and stuck on one of the growths, a bottle-thick metallic coil pressing out against the walls. The barbed feet dug in, a crackle of energy burst from the device, sending green sparks throughout the cab. The invading growths seemed to flinch.

In just a second, the hum of the engines, as well as the sickly glow, increased.

“Marlowe,” she murmured, drawing her pistol from its holster. He looked up at what had caught her attention.

The organic mound of machinery that had sprawled from the cab into the coal car had begun to move. Not quickly, not purposefully. It was more that it throbbed, as if some burrowing thing was making its way underneath the coiled and twisted surface. At the edges of the mound, wires emerged, sprouting out from the steel, stretching toward the newcomers, the invaders.

Aiming her pistol low, she fired across the front of the mound, the beam of energy frying the tendrils before they could progress further. The coiled mound shuddered, drew back. The humming of the engine took on a low, rough undertone, almost a growl. The light in the firebox flared red.

“I don’t think your trinket bypassed much of anything,” she muttered.

“Well, I tried,” he said, put out.

She lurched, falling against the side of the car. They hadn’t hit anything; the train was on a straightaway—no sharp turns ahead or behind. But the metal underneath her feet was moving.

The sides of the coal car bowed outward. The roof of the cab had swelled, and the cab’s windows warped into gaping circles. The very steel of the original train was expanding. Not melting, because there was no heat, but somehow the structure of the metal was changing as the Aetherian coils mounded inside the cab grew, puffed up, and expanded outward. In the cab, pieces of bodies bloated outward, and they looked as if they had been eaten, skin flayed, bone pocked with holes, blood entirely drained. The monster might have been sucking them for more power, using them to become ever larger. The bounty hunters who’d come to tame the beast had only helped it grow.

Meanwhile, Harry fired again at the snaking tendrils creeping toward them. Again, the locomotive growled in displeasure.

Marlowe’s device continued sparking bolts of green energy—diverting the locomotive’s power, as he’d explained. The engine coughed, and Harry felt a surge of hope that whatever was driving the train would be disabled. She watched Marlowe for his reaction—his gaze was grim, watchful. He did not seem optimistic.

The entire train, engine and coal car, bucked, and Harry was sure they’d jumped the tracks and were about to crash—which in her estimation would be a good thing, given the alternative. But no, the vehicle had literally shivered, like a horse dislodging a fly. Marlowe’s spider came loose from its anchor, slipped off the train, in between the two cars and onto the tracks where it was surely smashed to pieces. The strange red glow from the firebox pulsed.

“What now?” Harry breathed.

“I don’t know.”

That was worrying.

The crawling tendrils were increasing in size—and speed. She fired at the front line again and again—then shouted at a pressure on her wrist, her off hand, which was gripping the railing at the end of the car. A tube made of some rubberized, flesh-like stuff coiled around her wrist. She fell back, yanking away, but the tube only squeezed more tightly. Bringing her pistol around, she aimed some distance away along the undulating thing and fired. The tube flinched—squeezing yet tighter—and a stray charge from the ray blast traveled up the tube and tingled through her arm. Shivering at the shock, she blinked, shook her head, and tried to figure out what to do about this. Her hand was numb, immobile.

She slammed the butt of her pistol against a coil of tube lying against steel. No effect.

Behind her, Marlowe grabbed hold of her. She leaned into him as far as she could, giving him room to reach around with a very sharp-looking tool, like forceps with probes on the end. He stabbed this into the tube a few inches from where it held her, and the probes let off arcs of green energy. The tube went limp, and Harry quickly scraped it off her hand. The whole length fell to drag behind them on the ground.

“Are you all right?”

She had to open and close her hands a few times to get feeling back. “Yes.”

Ahead of the speeding train, a towering rock face loomed. “Marlowe, look!”

This was the tunnel Cooper had mentioned, a place where blasting through the solid granite of the Rockies had been deemed easier than going around. As they watched, leaning out from the car, the stone unfolded.

The tunnel would have looked normal to the riders who’d come to investigate. They’d have seen nothing wrong with the tracks, with the gaping mouth of the hole blown out of the mountainside or the rough granite within. But at the train’s approach, the stone changed, expanded, throwing out tendrils and wires, turning the stone into an alien maw. A match for the modified mechanics of the locomotive, the tunnel seemed designed to swallow the train.

“We can’t let the train enter that tunnel,” Harry said.

“There—that red light that keeps flashing from the firebox,” Marlowe said. “That’s what we want.”

The light seemed to come from a specific point, a globe emitting the glare like a light bulb. It flashed every time they did something to the engine—every time they made it angry.

“Do you have any idea how to accomplish this?”

He shrugged. “I’m not sure. But I would like to keep it intact if we can.”

To study it, of course. Exactly their mission. “And how do we do that?”

“We must get inside, of course.”

She pursed her lips and considered. “Well. How about I create a distraction?” She looked around, found her footing. Hauling herself up, she braced one boot against a railing and the other against the top edge of the coal car, one of the few spaces not yet overrun with the writhing mechanism. But the tendrils were coming closer, climbing up the sides, stretching out with their eyeless certainty.

Her balance on this perch was imperfect. In moments, she’d either be grabbed by the alien machine, or would be knocked off when the train came into contact with its partner at the tunnel.

She aimed her pistol over the locomotive, around its chimney, to the undulating walls of the tunnel reaching out to her. Firing, she kept her finger on the trigger and swept a steady beam across the machinery. The massed coils shuddered, flinched—and continued reaching out.

She spared a glance—Marlowe had taken to using brute force: a crowbar he’d stashed in his bag. He pried tubing out of his way, whacked at a bundle of wires writhing toward him, stabbed at an undifferentiated mass of machinery that had grown up over the coupling.

Meanwhile, the train slowed. Coils of bronzed wires reached up from the rounded sides of the engine to join with the coils reaching down from the tunnel, and the two sets twisted together, pulling the locomotive to a gentle stop, like an airship coming to rest against its mooring platform. A mollusk folding into its shell. In this new incarnation, the locomotive was home.

At the edge of the tunnel, the wire tendrils radiated from a central point, much as the locomotive’s adaptations grew from the firebox. That—that spot was key, and needed to be disabled as much as the light in the firebox did. She glanced at Marlowe’s progress; he was spending so much time battling the crawling mechanism, he had no chance to go after his target.

They had to do something drastic soon, or they would be overwhelmed, swallowed up by that alien mouth, just as those who had come before them had been.

“Marlowe—I’m going to try to give you an opening. Be ready!” Arms out for balance, she made her way along the edge of the coal car, from the untainted steel to the part of the train that had been overwhelmed with the Aetherian intrusion. Approaching the roof of the cab, she reached up and let a draping tentacle grab hold of her. Coiling around her left arm, writhing like a snake, it pulled her off her feet, raised her into the air.

“Harry!” Marlowe called.

“Go, just go!” she called back. He scrambled over the mound of gross mechanics and into the locomotive’s cab. Once he was under the roof, she could no longer see him. She turned her attention forward.

She kept her other arm, the one holding the pistol, low and out from her body where she hoped it would not be bound up in the coils. The thing had hold of her body now, squeezing her legs and torso with a constant pressure. It wasn’t painful—as if it knew she was a living thing and had no wish to harm her. And yet it was drawing her inexorably upward, into its central maw.

That was her target.

This was a matter of timing: She had to maintain her range of motion and some semblance of calm when she reached that central point. But the number of tentacles locked on to her was increasing. Indeed, more seemed to come into being before her eyes. Soon, the thing would envelop her completely. She lunged.

Using her very bonds as leverage, she thrust forward her right hand, stabbed her pistol as far into thing’s root as she could—the distance was considerable, more than she was expecting, because there was no central mass. The thing resembled a ball of yarn, threads coiled endlessly upon one another. The mass of threads pressed against her, seeking to immobilize her.

While she still could, she fired the pistol in the beast’s heart.

There was an explosion, and she fell.

The tentacles all loosened at once, releasing her at the precise moment she was high in the air with nothing below to break her fall.

The pistol was gone, destroyed. Hands free now, she grabbed one of the flailing tubes. It held, and she swung, smacked against the granite mouth of the tunnel—but it was just a tunnel now, with strange metallic vines hanging over the entrance. No longer a mouth. Her right arm ached—the blast from the gun and subsequent explosion had shredded her glove and the sleeve of her jacket. The fabric had only partially protected the skin underneath, which was pocked with cuts and bleeding.

Below, the train had stopped. She still couldn’t see Marlowe in the cab. Hanging from her length of metal, she waited, watched for movement. Didn’t see any.

“Marlowe!” she called. No answer. “Marlowe! James!”

“Yes?” He emerged, straddling the coupling between cars, looking up at her. He had the crowbar and pliers in one hand, and something odd and alien in the other.

She slumped, relieved, and lowered herself down the vine until she was resting on the roof of the cab. Here, too, the Aetherian appendages seem to have died in place. She pushed them away, and they dropped to the ground. “This is entirely bizarre,” she said.

“Yes. What do you think of this?” He handed her the thing he was holding, the component from the firebox.

It was hexagonal in shape, the size of her two hands together, and heavy. An intricate network of tiny wires ran across it in a mind-breaking geometric pattern. Given time, she might make sense of it, but at the moment it seemed a blur. She had trouble focusing on it.

A reddish glow suffused the device, and several prongs around the outside of it were probably connectors. It was meant to be attached to something else. Somehow, it had made its way into the firebox and found a home there.

“Just a moment,” she said, looking back up at the cavity where she’d discharged her pistol.

She grabbed back hold of the tentacle she had climbed down on. It slipped, dropping—starting to come loose. Her arm was bleeding more profusely, the lacerations unhappy with her exertions, but she ignored the discomfort. Carefully so as not to dislodge the vine further, she climbed, bracing her boots against segments of material that had grown together.

Back at the edge of the tunnel’s mouth, she could examine the tentacles here further. She drew her knife out of its belt sheath. She couldn’t cut through the metallic tendrils and coils, but she could pry apart the segments, and the metallic appendages dropped away, giving her better access to the hollow place in the rock from which the tendrils emerged. Almost a cave, tucked away where no one could see it.

She traded the knife for a hand lantern from her belt pouch and examined the interior. The surface was scorched, stripped and burned by the pistol blast. But yes, there was a space, and inside were the scattered and melted remains of her pistol, and of a device much like the one Marlowe had shown her. She collected the pieces, tucking them into her pouch. They were still warm.

She dropped back onto the roof of the cab, then across the coupling and into the coal car, where Marlowe was clearing away tentacles and segmented tubes. The locomotive was appearing more like its old self, and less Aetherian monster, by the moment.

“I think there must have been a cave or some pocket in the mountain side,” she said. “It might have been covered by debris until the rail company came along and blasted the tunnel. An Aetherian craft or being might have stashed away some artifact, by chance or intent. Maybe they meant to retrieve it later. When it was exposed, it was activated somehow.”

“Harry, you’re hurt,” he said.

She glanced at her arm. “Yes, but I think it just needs a bit of washing off—”

“No. Here, sit.” He took her arm and guided her down to sit at the edge of the car. He touched her forehead; his glove came away bloody. She realized that throbbing wasn’t nerves or the noise of the explosion rattling in her brain. She’d been cut by a bit of shrapnel.

“How bad is it?” Now that she noticed it, blood seemed to be running down her face. She didn’t have time for this.

His expression furrowed as he leaned in to look, producing a handkerchief to dab at the mess. “You may need a stitch or two.”

“My grandmother will never forgive me if I’ve ruined my face,” she muttered.

He chuckled. “Not possible, Your Highness. Here, hold that.” He gave her the handkerchief to press over the wound.

His touch lingered, resting on her chin a moment as he turned her face and seemed to study her eyes very intently. He was quite close, and her heart raced a bit. She would not lean in, not even a millimeter.

“Your pupils are the same size,” he said. “Can you follow my finger?” He held up a hand and tracked it up, down, left, right. Obediently, her gaze followed the movement. “I don’t think you’re concussed, so that’s good.”

“Yes, very good,” she murmured. Her chin felt cold when he finally let her go.

“Your hypothesis seems reasonable,” he said. “Given what I think this might be.”

He set the device from the firebox in the open. She produced the pieces she had retrieved, laying them alongside. Difficult, trying to make out what the thing had been. Whatever energy or glow it had had was gone now, but the same complicated pattern of minute wiring was visible on some of them. They were a matched set. The intact device pulsed a little when the pieces came along side it.

“I think,” Marlowe said, “that these are a set of devices to create automation in machines. Self-directed automation.”

“It’s . . . a mechanical brain?”

“If you like.”

“Then you’re saying it was alive.”

He paused, furrowed his brow. “I don’t know that I would go that far. The thing needed a machine to control. The locomotive came along. You remember what Cooper said, they’d switched a steam engine for an adapted one—bug-rigged. Like called to like. The artifact might also have had some component to defend itself. Hence our poor victims down there.”

Defense—a weapon that could defend itself? Oh, this was dangerous indeed.

“But it had a will?” she asked. “Was it intelligent or merely carrying out some . . . artificial instinct? Like the German’s mechanized troops?” Comforting, to think this was simply another version of the same kind of controls that operated the fearsome mechanical beasts that the Germans sent into battle. But this . . . this had been something more. The alien-controlled locomotive had seemed to have intent. No one had set the train on its path. No one human.

He tucked the device in a pouch and gathered up the pieces Harry had found—placing them in an entirely different pouch. “You wanted to make this expedition to learn more about Aetherian technology, to discover Aetherian mechanisms no one has seen before. I think we’ve succeeded here.”

“But what are we going to do with it?”

“For now—lock it away and carry on.”

• • • •

They spent the rest of the afternoon clearing the train of its extraneous additions, stashing tentacles and coils of wire—and human remains—in the coal car. Marlowe was able to bring the original Aetherian-adapted engine back to functioning order. The thing hummed normally, and its green glow was exactly the shade it should have been. They spent the night camped by the tracks and didn’t sleep very well. In the morning, they set off back to town. Without its brain, the locomotive was simply another Aetherian-adapted train, clacking mundanely as it ran back toward Alamosa.

They arrived back at the station at eight in the morning, four hours ahead of schedule. Mr. Cooper was waiting on the platform, all astonishment.

“We’ll be collecting your bounty, I think,” Marlowe said, cheerfully hopping onto the platform after shutting down the engine and letting the locomotive roll to a stop. Harry followed more slowly, aware of her bandaged head and arm and the stares she was attracting.

“What? How?” Someone had sent for Finch and several other town officials as well. They lined up like a jury, staring.

“Very carefully,” Harry said. “And you’ll need to call an undertaker.”

• • • •

They got the bounty, which seemed ridiculously anti-climactic to Harry, since they hadn’t done any of this for money, and what she had seen was so much larger than mere money. But they had to maintain their cover story. Harry put her foot down and insisted they use part of the bounty to take rooms in the local hotel. They ate a very nice hot meal, drank the establishment’s best bottle of wine—a mediocre burgundy—and had very hot baths. The next morning found them back at the Kestrel. They spent an hour or so packing before unmooring her lines. Harry was uneasy.

“Was it alive? Not just alive—but had the Aetherian pilots somehow left a piece of mechanical intelligence behind? A piece of themselves?” She couldn’t stop asking the question. Her bandages itched, and resisting scratching them was making her cross.

Marlowe sighed. “Yes, it probably was alive, at some level. It grew, it had self-motivation. But I’m not sure it was any more intelligent than an earthworm. It was a machine, Harry. Whatever else it could do, it was mechanical.”

“I can’t help feeling that we have broken something that can never be repaired.”

“It was trying to kill us, don’t forgot.”

“Yes. But I wish . . . Well. If it had been truly intelligent, we could have found a way to talk to it, yes? I would have liked to talk to it.”

They finished stowing gear in the chests and cupboards on the Kestrel. The pieces recovered from the phantom engine got their own locked chest—far away from the Kestrel’s engine. After checking the engines and gauges, examining the bladders for tears, repairing the one or two they found, they filled the bags with gas and pulled up stakes and lines. Marlowe climbed the ladder as the ship rose. A crowd of locals looked on with gaping curiosity. Some of the children waved, and Harry didn’t wave back. The engine pulsed and whined, sent a fresh surge of gas into the bladder overhead, and the ship rose, up and up until the buildings below looked like toys made out of balsa.

“Where do we go from here?” she asked.

“West,” Marlowe said, looking in the direction to where the sun would set in another six hours. “Always west.”