The south of the city is ours. London Bridge has fallen down, and Waterloo has gone under. Borough, Lambeth, Fulham, these are our places, and east all the way to the sea. Your little island enclaves are almost all gone now. Chelsea and Westminster Hospital’s bleached bones are emptied of you. We starved you out of the Passport Office on Belgrave Road, and when we came in force to the Victoria Palace Theatre you left of your own accord, paddling frantically on rafts made of doors and tables. Even the Natural History Museum is ours, and we crawl up from the shallows to step into its vaulted fastnesses and stare at the collapsed wreckage of its model whale. We will take better care of its relics than you.

We are on the move again. The sounding song echoed its call to arms through the drowned arteries of the Underground. The clans are gathering to take back Knightsbridge from your unwashed hordes. These are our places now; you have forfeited your stewardship of them, but still you come down to the water’s edge, ragged and starveling. Still you come to net our fish, to break open our crab pots and our traps with your hungry hands. You come to the edge of the water and look south towards the sunken treasures of Sloane Square and try to pretend that it is all yours again.

Well: We are coming for you, all our warriors. We hump and sluice along the city’s new canals of Lyall Street and Lowndes Place, and we gather within the broken shell that was the German embassy. These names you bequeathed to us—we read them on your monuments and street signs. I wonder, when you see those letters, do you also know the sounds they make, the history they hide, or are they just markings on a wall, now? Do you have even so much of your past left to you as that?

But better than the surface streets, where the water runs shallow and where some of your clever monkey people might yet ambush us, better than this is the Underground, the lightless sunken net cast beneath the streets of London. We flurry through its great arteries, rising at each station to catch our breath, moaning out our low sounds that let us feel our way along the walls. Calling out to each other in voices too deep for you to hear and that sound the width of a borough; we take in air at South Kensington and plunge into the darkness.

Some of us will erupt from the surf at Hans Road and Walton Street; the rest of us will be at your back, crawling from the abyss that is Knightsbridge Station with our spears and our crossbows and our sharp, sharp teeth. And we will cut a wound deep enough into your collective memories that not a one of you will dare come back within sight of Tyburn Brook or Kensington Road for a generation. And when that generation is gone, the waters will have swallowed Knightsbridge whole, colonised it for our way of life.

• • • •

They called him Doctor Deacon, the man who brought us into the world. You have another name for him now; he has become part of the impoverished pantheon of devils that comprise most of what you remember about the world before the waters. Back when your ancestors were still denying that the ice was melting, Doctor Deacon was hard at work: creating us; a legacy fit for the future that everyone saw coming and nobody professed to believe in. We have our stories of those times: how the wise men told you of the flood, but you were too mired in sin to so much as built a boat. We keep a library high and dry near Vauxhall, and I have seen the writings from those days. You were always complaining about the weather. “Who wouldn’t want a few hotter summers?” you said.

All the land was yours, and back then that was an unthinkable bounty. You didn’t know what you had. You ransacked the seas and you tore up the earth and covered it with the concrete and the tarmac that will long survive you. You forgot, as the ice began to melt, how your whole civilisation was built about the rim of a bowl, all your great coastal cities, and what happens when the bowl begins to overflow?

Doctor Deacon knew, and so, even back then, long before the tipping point was reached, he was hard at work. You laughed at him, the stories say—though later, when you found out what he had done, the laughing would stop. In those days, sunk in deep history now, your wise men were capable of many things. You could take the living features of one creature and gift them to another: immune systems, tissue regeneration, the glow of a jellyfish in a cat or a rabbit.

Our progenitor sequenced the life-code of your mammal cousins who took the waters as their home. And he took your children and he started his terrible work, his wonderful work, the work for which we and you both remember him. We remember him more fondly, I rather suspect. In our stories he is a shaman, and his totems are Seal and Sea Otter. In yours he is malevolent and mad and, whilst I know that he loved us, I cannot wholly argue with the second. He must have been a little mad, but mad in the way that those touched by God are mad.

• • • •

We mass at Knightsbridge Station, just below the surface, taking turns to breathe at the half-sunk steps. Knightsbridge is a peninsula now, caught between the burst north bank of the Thames and the Serpentine. You should know better than to go there, really, with your escape route narrowed to that single land-bridge, but the waters there are fertile, some of the best of all that great expanse of shallows that was Central London. We farm there, our weed and our fish, our shells and our crabs, and where we farm, you come to steal from us. Shallow seas are paradise for my people, and the world has so many of them now, where the rich earth has been taken from you. It wasn’t as if you were taking care of it, after all. If you had been better custodians, we wouldn’t be here. There wouldn’t have been a need for us.

I go ahead, hauling myself up the ridges of the stairs. Out in the open air, the red sun in the west silhouettes the broken skyline. Evening is upon us, and you have outstayed your welcome. I am awkward on the hard ground for a moment before I find my feet. There is still something of you, in the way I stand. My spine is more flexible, my posture more bowed; my neck is long, my head streamlined. My eyes are huge dark pools that pierce the gathering dusk far better than yours. Where you scavenge rags to hide your bare bodies, I have my oil-thick fur.

My hands are like yours, though: part-webbed, but I have your fingers and your thumb, dark and naked. Or perhaps they are otters’ hands, after all. I would prefer that to be the case.

I slink from the toothless maw of Knightsbridge Station, humping my lithe body from cover to cover: not as nimble now I am on the land, but I can stalk two-legged prey with the best of them. Your sentries do not see me, between the drawing dark and the glare of sunset.

There are so many of you! I am always shocked to find there are so many left, and these are just the mass of you in this one place and time. There are numbers we have learned, for how many humans lived on the earth when Doctor Deacon began his work, but they are meaningless. They are numbers that nobody should have any use for. I know there must be far less of you now, but still . . . so many, crawling like maggots across the Knightsbridge peninsula, netting and clawing at the water’s bounty, stripping the littoral of everything edible. Your habits have not changed since the waters came.

I wait there, watching you, trying to see you as something other than a composite, consuming mass. You are pale and filthy, and I can smell the thin, sour reek of you from here. And you are thin—limbs like sticks, faces like skulls. You cluster together in your little clans: You have brought your whole families for this day at the seaside. I smell the smoke of your little fires, but many of you just tear at the fish with your teeth, too hungry to wait.

I watch your children. Even hungry, even desperate, at this trailing loose end of your history, they are still children. They play and jump as ours do; they fight each other as ours do; they splash in the water, eyes bright with curiosity. No doubt you love them, just as we love ours. You want the best for them, now that your parents and their parents have ensured that you will have only the worst.

I wait too long, watching your young. For all that we are children of a different god, I cannot see your children without feeling the stir of pity in me. We were all human once, and our creator left alone those things that let us think and feel. My heart, my lungs, my blood, my bones, these he improved, but that part of me that loves, he left alone.

But all these lands under the water’s shadow are ours, and we have hungry children too. Your busy hands are taking the food from their mouths even now. I shake off my pity. I stop watching your children and instead I mark your guards and your sentries. The dusk has set in, and it is our time.

• • • •

You tried to wipe us out, when you discovered us. Deacon was an old, old man by then, but you took him up and paraded him to his show trial. You raided his laboratories and you destroyed his samples and you confiscated his machines. This was even when the waters were rising, even when you were staring into the mouth of your apocalypse. If you had stepped back then; if you had looked into the future and seen something you might share, then we might not be killing you and driving you away from every shore. But you called us abominations. Some of you invoked divine writ and some of you invoked medical ethics, but none of you could countenance the idea that you were no longer unique. You scorned Doctor Deacon for playing god.

But by then, he was not alone. Persecute as you might, there was always someone carrying on his work. He never knew, by the time you hounded him to his death, but his task was done. His future race was already multiplying in the waters of the world.

I wonder, sometimes, how he saw it. Unhappy though the thought is, he probably did not expect this war. Perhaps he hoped that we would live among you, that we would help you and feed you and protect you when the waters swallowed your cities. Perhaps we would have done, if you had only let us.

Some of us wonder, still, if we might reach some accord with you, but we can barely even communicate any more, and each generation brings more reasons for hate on both sides. And we do not need you. You have nothing to offer us but more mouths to feed.

• • • •

So I go back to the dark waters of Knightsbridge station and give the signal, booming into the tunnels that will amplify the resonance of my voice. My orders rumble through the sunken fastnesses of the underground, and roll out across the drowned flats of Belgravia, coursing between the jutting teeth of all the buildings you abandoned, or that we drove you from. With the echo of my own words buzzing in my ears and on my skin, I launch myself across the trivial boundary that separates land and water. We are going to war.

We flood from the station. I can already hear the screams and cries as you spot us. My crossbow is cocked and loaded: made of bone and plastic, strung with sinew, the quarrels headed with shards of glass or found metal. The wealth of a fallen civilization is beneath the waves for us to salvage.

Most of you are fleeing, funnelling down the peninsula back towards your land, towards those parts of London that the waters have not yet blessed. You live out there, in your teeming, starving hordes, in your rookeries, your brutal, feudal kingdoms: Hallfield, Marylebone, Soho. You spend more time fighting each other than troubling us. I watch you squabble and panic and get in each other’s way. The main wave of our people is already bursting from the water’s edge. Spears jab at your pasty skin; clubs whirl.

For just a moment I stop. My earlier empathy has a hook in me still. I see you scoop up your children in your thin arms. I see that some of you stay behind to cover for the rest, a noble sacrifice. I see you do all the things that we would do—that we have done—with our positions reversed. And we were you, once. Before Doctor Deacon reworked us for this new world, our ancestors were your ancestors. We were only human.

Then I hear the roar of a gun, and I shake myself from my trance and go to work. The sounds are dull to me—being out of the water is like being half deaf. I see the flash: My cousin Enzo goes down, and a couple of others, before the shooter is silenced. You have more of those ancient weapons, but not so many more, and how many bullets? And how many weapons have been maintained in the long age since their manufacture? You brandish plenty of them, but I hear few shots, and each one is ammunition you can no longer replace. How long before those precious firearms you are so fond of are nothing but talismans, their true use forgotten?

I aim, loose, reload, and aim again. This is my seventh skirmish with your kind. I have learned to fight out of the water, to judge distances, to ignore the dry air, the heat, the dust. It is for you that I endure these things, because you will not know your place. Your place is inland. Your place is in the past.

The waters run red. You will steal no more of our labours. Those who survive will remember the terror that came from the sea. We will not find you here again this year, perhaps the next. The year after, maybe Knightsbridge will be under as well.

I watch the last of you run. Our wounded, our dead, are being pulled back to the water, to be given all honours and cast into the current. Your dead must be disposed of as well. We will haul them to the broken heights of your buildings; let the things of the air pick at you; let the flies hatch from you. At least that way you will give something back to the world.

We will drive you into the parched places, the barren places. Should we have sympathy? This is the world that you made, after all. Some of us say, how could you have realized that you were making it for us to live in? But those of us who retell the old histories know better. You could see the dam groaning with the weight of the waters, even before Doctor Deacon set out to build his species anew. You could have stopped this; you didn’t have to offer us the world. Don’t cry to your dead gods now that we come to take it from you.