This room was designed to be perfect. But in the mornings, if I'm quick, I'll catch the way the sunlight hits the floor at an angle, exposing three names in the wood: Muriel, Star, Summer.

The girls who came before me.

The rest of the night room is ordinary: four walls, a stark egg-shell white, with a single canvas hanging on the fourth–it is a watercolor picture of what they tell me is the ocean.

The floor tapers off into a small, rocky pool, closed off from the main pool with a wrought-iron gate. In the corner is a bunkbed, its top bunk unslept in, the white sheets tucked smoothly between the mattress and box springs. Beside it, hidden between the bed and the wall, is the makeshift nightstand made from Muriel's old books.

Reading is key, she would say. Your body might be trapped, but your mind is always free to wander. Maybe this was her plan all along. Maybe she knew that it wouldn't just wander, it would learn. I know now why the night rooms are plain, why the walls are stark white and the dark floors unpolished. Beauty, grandeur–it isn't meant for us.

The morning bell chimes. I sit up like clockwork and pull on my swimsuit, a sturdy two-piece made from clear-cut green gems. The tail goes on next, lightweight silicone coated in scales, each one as polished as the next. I fasten it at my hips the way they taught me in the facility and lower myself into the pool.

At 9:15, the iron gate lifts. Beyond it sits the other world, the one made for them: a two-story aquarium filled with gallons of water, enclosed with tapered glass. I dive to the bottom and swim through the gate, into the enclosure.

There is an ugliness to the perfection, to the order. Each piece of coral is the same shade of salmon, each drop of water a cobalt hue. Every detail, from the choice of foliage to the texture of the rocks, has been engineered to please–including me.

It is why the plunge pool is my sanctuary. Tucked away on the surface, it is a small, circular pool that spills over into a series of waterfalls and smaller rocky pools.

The space either side of it bursts with foliage: thin, feathery plants lurch in different directions, broken only by the odd burst of pale pink blossoms. Around the edges, small tufts of greenery sprout through the concrete, a mistake, I'm sure, but the sight of it brings a smile to my lips–nature's little way of rebelling.

From up here, it is impossible to see the other girls, but I imagine them below the surface somewhere, whispering about the guests. We have learned to speak without making a sound. It doesn't travel as well under water, so we each learned to lip-read. In this way I learned more than just their names – I learned how to love them.

By eleven, the sun has broken through the clouds, coating the aquarium in a pale shade of gold. The park is always busiest at the weekend, and the windows are crowded with guests. I swim to where the majority are gathered, fix on my smile, and skim my tail along the glass.

A young boy flashes a wonderful smile. He is crouched on his knees, nose to the glass, eyes wide with wonder. He thinks there is something special about us, and maybe there is; maybe there's beauty in being engineered. But if there is, I don't see it.

Across the aquarium, Jewel watches me. Locks of red hair form a veil around her face, from which two emerald eyes peek through. She flips herself away from the rocks and shoots toward me, leaving a whirlwind in her trail. The boy turns away from me to focus on her; when Jewel looks back, her eyes are triumphant.

Others crowd the window now, fighting to get to the forefront. The boy is pushed back and a young, wiry girl takes the space he left behind, pressing her nose to the glass.

An older gentleman stands beside her, resting his hand on her arm. He lifts that same hand, moving his finger in a circular motion I'm certain means he wants me to spin for him. I do, making sure to keep my chin up and my neck elongated, the way we were taught in the facility.

The man turns once I've finished, spotting Crystal in the distance. He starts with her face the way most of them do, skimming the distance between her eyes and lips, trailing the length of her collarbone and stomach before reaching her hips. It is here that they linger, following the ridges of her tail with a childish wonder. He knows it's not real, this world they've created, but sometimes, it's easy to forget.

At some point, I break the surface to catch my breath. We can go around an hour before needing to inhale, sometimes longer. Marine World would have us go all day if we could, but even we have our limits.

Crystal is perched on the ledge of the plunge pool, staring at a guest. He is young, though possibly older than us, with short blond hair and pale green eyes. She flashes him a smile, then flips into the water to face me.

"His name is Tom, he's a Scorpio and his favorite color is blue," she says.

I glance at Tom with an eyebrow raised. "He looks more like an Albert."

She bursts out laughing, a warm, hearty sound that sends warmth through my body. "He does not," she says, pushing my shoulder. "Why do you always ruin it?"

I smile slightly. "He does, and his favorite color is lilac."

She furrows her eyebrows, an expression that would look menacing on someone like Jewel, but makes Crystal look all the sweeter. "Okay, you're not allowed to play anymore."

"How can you stop me from playing a game I created?" I ask, but it's not technically true. Trainer Alison taught me this game six months ago, and we've been playing it ever since.

Jewel calls it a hopeless game. What's the point in a game where there are no winners or losers? But the fun isn't the game itself, it's in what it stands for: a break from routine, a moment between us – a tiny act of defiance.

At five, the Experience starts. From what I have seen, the aquarium is shaped like a rectangle and made of ten compartments, with two sets of experience rooms either side of the aquarium. My Experience room is small, with unnatural blue water and a thin, parched palm tree sprouting from a strip of sand.

Perched on one of the palm leaves this morning is a wiry bird with a light brown face, a rounded, white belly and a short, brown tail. It hops from branch to branch, examining the leaves with a freedom I can only dream of. "Lucky," I mutter. Then I glance over my shoulder. Maybe our thoughts aren't even safe.

As though intrigued by my presence, the bird lets out a brief, high-pitched chirp. I make a sound that mirrors his, and the bird falls still. He tilts his head, chirping again before awaiting my reaction. He must think we speak the same language, him and I; he doesn't realize it's only a trick.

Trainer Lucy walks in and stands by the ledge. Her fair hair is up and she's wearing her wetsuit, which is so tight, the material looks like a second layer of skin. Slowly, she tiptoes along the narrow ledge between the pool and the safety railing, stopping to look at me.

Her eyes are pretty. Green, with little flecks of yellow and brown, like the color of leaves in the beginning of Autumn. Sometimes, I think it is with these eyes that she often says the most: a tender look, a flash of sympathy–like us, she has found a way to bend the rules.

I get a little girl for my experience: a chubby, pouty thing with a sour expression. I give her what I hope is an encouraging wave, but she scowls in return.

"Dana's been grumpy all morning," her mother says. "She wanted to swim with Crystal but her slot was already booked, and this is our last day at Marine World."

I shouldn't care, but hearing this causes my heart to sink. Why is it the children prefer the others over me? Am I not pretty enough? perfect enough? It is not for the sake of pride or vanity that I worry–it is self-preservation. It's been drilled into our heads since we left the facility that our purpose is to please the guests. If I can't fulfil such a purpose, will I be the next to disappear?

Slowly, the girl steps forward to study my tail. The girls and I might share similar features, but we have each been given a unique color tail that is distinctly our own: Asia's is a deep yellow, which contrasts with her dark skin. Crystal's is the same pale blue as her eyes, Jewel's is as crimson as her fiery red hair and my own is mossy green, dull against my tan skin. Briefly, I wonder if this is the reason children prefer the others over me: I am the least unique of all.

I hold out my hands as the girl inches forward. Then, carefully, I take her by the waist and pull her through the water, flipping my tail to propel us. In this way, I am able to lose myself in the rhythm: forward, backward, forward, backward. I've performed this routine a thousand times. More.

When time is up, I propel a giggling Dana back onto land, where Lucy escorts her out. Then I swim to the gate separating my room from Crystal's and press myself to the bars. Watching Crystal is how I imagine it must feel to watch us as a guest. I can understand why they adore us, why they pay to watch us dress up in a tail. Crystal is like something from one of the books on my nightstand, something that doesn't quite belong in this world.

She takes her guest through the rest of the routine before dipping below the surface. We're allowed to take guests under for a second or two–a harmless thrill–but that is all. The guests can't hold their breaths like we can, which is why when Crystal doesn't resurface, I freeze.

A few seconds pass before she breaks through the water, her guest unaware of the break in protocol. It doesn't matter. As soon as the Experience ends we are ordered into the main aquarium, where Trainer Alison is waiting by the steps. She kneels against the safety railing, pulling her dark hair back into a ponytail.

Out of all of our trainers, Alison is my favorite. Maybe it's her smile, or the way her eyes light up when she sees us, or her willingness to break the rules just a little, but there is something about her that makes this place bearable.

With her hair tied back her hair, she stretches her neck, clicks her knuckles and then turns to face Crystal. "Your Experience trainer told me you kept a guest underwater for longer than you should have," she says. "I'll have to go through the routine with you again." She runs a hand down her face, as though this is the last thing she wants. "Your routine was perfect, Aura. You can head on into the night room."

She barely looks at me, so I hover for a second. "What's wrong?" I can be forward like this around Alison–she is more like a friend than our trainer.

For a second, she smiles. You're always so observant, Aura. That's what she's probably thinking right now, that I've picked up on something, a change in her mood that she's been trying to hide, because it is not just us who have a role to play, it is her, too.

"Come on," she says, turning away. "Let's get started."

I swim into the night pool, and Alison presses a button on the wall so the gate closes shut. Usually, I'd climb out and head straight on the treadmill, but this evening I watch through the bars as Alison takes Crystal through her sequence. I don't know what it is that makes me stay, exactly. I just have this feeling that something is wrong. Not just with Alison, but Crystal, too.

For the first few minutes, everything is fine. Crystal follows the routine as normal, but when they get to the underwater part, her stride is five seconds longer than permitted. I bite at my cheek. She knows this routine like the back of her hand–we all do. It doesn't make sense that she's messing this up, not after what happened to Muriel.

Alison pushes herself through the water, but instead of doing the same so that the two can talk on the surface, Crystal grabs Alison's foot. For a second, in the pale evening light that streams through the water, all I can see are her dark green eyes, wide with fear.

Then instinct kicks in. She flails against Crystal, kicking, thrashing, anything to gain back control. But Crystal, like me, was built to be strong. So I know how this will end.

I scream something through the water, hoping to get their attention. Water fills my lungs and burns in my throat, but I don't stop screaming. Crystal ignores me and wraps herself around Alison, who by now has stopped struggling, stopped fighting. I thrash and scream, scram and thrash, even though it is futile. I am watching the life drain from Alison's eyes, and I am powerless to stop it.

Alison's body finally grows limp, and Crystal relinquishes her grip. She turns to face me, mouth closed, expression calm, and just like that, I understand.

Crystal had planned this.

Hey readers, hope you enjoyed!! 🧜🏽‍♀️

What country are you reading this from? 🇬🇧