I stood rooted to the deck, mere steps away from her, unable to do anything except stare.

Her bottom half wasn’t visible. If we didn’t know any better, we could have mistaken her for a young woman. But we did know better. We knew from the waist down she was mutated—a demon.

“Hanu aii,” she said. Her high voice rolled as smoothly as the waves.

The overlarge eyes found mine, unnaturally vivid, a flare I couldn’t look away from. She motioned me forwards with long, white fingers. A soft noise came from the base of her throat, almost like purring.

I stepped back. She was trying to hypnotise me.

She dropped her hand, seeming to realise her seduction wasn’t working. Her eyes hardened, and she looked around as though suddenly aware of the rest of the crew.

Nobody said anything; we only stared at this benign creature. She was just a girl our age, and vastly more beautiful than any of us. But from the waist down . . .

Dani stepped forwards, shoulders squared.

“Stay back!” she yelled to the mermaid, aiming her crossbow.

The mermaid scrutinised Dani, and though her smile fell, not a trace of fear showed in her enormous green eyes.

Dani tightened her grip but didn’t fire. The crew seemed to hold its breath. Something felt amiss about sending a bullet through this teenage girl. Was this really what we’d come here to kill?

But then the mermaid’s lips curled back, and before my eyes, her teeth changed. They lengthened into points. A gust of wind swept her hair forwards so the jet-black locks billowed around her, and the beautiful young girl looked suddenly feral. She screeched, a high-pitched wail that echoed across the water.

The instant I realised how immobile we’d become, she launched herself over the railing and landed on the deck with a thud I felt in my legs. Movement erupted around us; dozens of hands and faces appeared between the railings on all sides.

I had to admire Dani’s reactions: before my muscles even responded, she shot the black-haired mermaid through the heart. The mermaid choked to a halt, crimson blood splattering from her chest. But we’d all been transfixed for too long—were we hypnotised?—and at least fifty mermaids scaled the Bloodhound on all sides.

I stared at Dani’s victim. Head bowed, she tried to hold herself up with trembling arms.

An earthquake rumbled the deck. Around me, the mermaids descended on the ship with a dexterity I’d never seen.

But the girl! I turned back to her. She was dead. Her glistening corpse lay face down in a spreading pool of blood.

She isn’t a girl.

The proof lay in front of me. I could see the demon’s tail.

A smell met my nose, infusing me with panic, bringing forth a memory I’d buried for so long—rotting fish, smoke, seaweed—the smell of a mermaid freshly defiled by iron.

Blacktail reacted beside me. She fired at a mermaid and ran for the main deck, already loading another bolt.

My hand tightened around my crossbow. Did I just witness a murder, or a step towards freedom? That didn’t matter now. I forced my eyes away from the pool of blood, cranking the lever and notching a bolt with numb fingers. The other mermaids advanced, and they moved more quickly than I imagined.

One of them thundered onto the deck across from me. I stepped back, hoisting my crossbow to my shoulder. Her eyes locked on me—on my throat. Time slowed. The girl’s smooth body transformed before my eyes . . .

And more than ever, without a mask of darkness, I understood why they were called sea demons.

Her eyes were red the whole way through, deeper than blood, without a pupil or the surrounding whites. Her heavy auburn hair fell over her face and shoulders but never covered her diabolic eyes. Her skin was rotten, the colour of seaweed, and even the shape of her ears reminded me of the slimy algae that often washed up on the beach.

She moved across the deck with a jarring stiffness; if I hadn’t known she was a mermaid, I would’ve thought I was witnessing a girl possessed by the devil. She used her arms to drag herself forwards, rigidly shifting her weight, locking her elbows to keep her body upright. With each shift, her bony shoulders seemed to pop out of place. One of her hands clawed the deck—the hand of a fish, webbed with clear skin between the fingers from grooves to knuckles. Her other hand gripped a weapon, a conch shell, and she smashed it into the deck as though the planks of wood were just as much her enemy. The way she advanced was a practiced technique, swift enough to catch a fleeing human.

My lungs contracted frantically; my limbs numbed of all feeling. This was no human. This was the furthest thing from a human.

Shoot it, Meela!

The sound of whizzing bolts, thundering feet, screaming girls, and screeching mermaids pounded in my ears. I leaned my head down to aim. My frozen muscles finally responded as the demon drew near enough to attack. I aligned my sight with her chest, and pulled the trigger.

The bolt shot wide of her heart and pierced her shoulder—enough to fatally wound, but not to instantly kill. Still, she advanced.

Cursing, I pulled another bolt from my quiver. My hands must have been shaking.

Without warning, the demon threw her conch shell at my face with the strength of a cannon fire. I ducked, but felt the tip slice across my scalp. Pain exploded and warmth oozed from the wound. My knees weakened at the feel of my own blood.

Anger shot through me—mostly at myself for wasting so much time. I straightened, jammed the bolt against the shaft, and paused for a millisecond to aim.

Before I even finished pulling the trigger, I knew I had her. The bolt hit her dead in the throat. Her mouth opened like she was trying to scream, but no sound came out. I gasped, turning away as the blood spilled from her like a geyser.

My muscles had awoken, vibrating with adrenaline. Blood pulsed into my limbs and forced away the queasiness that had taken hold.

Another demon lunged at me from the side. I spun and fired without hesitating. It hit her in the heart and she collapsed. But already the next demon was upon me, nearly wrapping her slimy fingers around my ankle. I shot her through the top of the head. Blood splattered into my eyes.

Blinded, I stumbled backwards, reaching into my quiver for another bolt. But no other mermaids came. Screams and hissing crossbows filled the air. I wiped my face on my sleeve and scanned the corpse-laden deck.

Dani was at the fore mast in the thick of the action. She stood on the boom, firing downwards, battling four mermaids at once. Rocks and blow darts peppered her. Some knocked her off-balance and darts stuck into her arms, but she was quick. She reloaded smoothly and without pause, firing at each of her attackers in turn. She pulled darts from her skin only to launch them back at the mermaids.

More approached but three other girls took them out in sequence. Beside them, Linoya roared at the demons, swinging her crossbow and egging them to come get her. Beside her, Nora shot them down with lightning-fast reactions.

At the edge of the deck, Eyrin had dropped her crossbow. A brown-haired mermaid swung a jagged spear—once a harpoon, perhaps, but ravaged by the sea and covered in sharp barnacles. Twice, the spear caught Eyrin in the arm, and bloody gashes spilled open.

I ran forwards, but before I could raise my weapon something whizzed past my nose and I turned in time to see a demon rushing towards me with a fistful of short spears. She hurled another with blinding speed. I ducked, keeping my sight aligned, and pulled the trigger. The bolt hit her in the stomach before she could throw another spear. She made a wet coughing sound and buckled over.

I turned back to Eyrin. Her assailant raised an arm to strike again. I didn’t have time to get there. I rooted my feet on the swaying deck. My bow steadied as I exhaled. I fired.

The bolt buried in the mermaid’s ribcage. She fell to the side, dead instantly. Eyrin scrambled backwards.

Another mermaid had been waiting. She launched herself at Eyrin with a barnacle-covered rock in her hand and knocked them both to the deck. I slammed another bolt against the shaft. Eyrin shrieked. She tried to push the mermaid off but the mermaid had her pinned.

I aimed—but the mermaid’s arm was a blur. She smashed the rock into Eyrin’s temple. I screamed and let the bolt loose too soon. It shot wide, skimming the mermaid’s tangled mess of hair. She flinched but didn’t look.

Eyrin went limp. I loaded my crossbow with a violently shaking hand. The mermaid gripped Eyrin’s head with a webbed hand and brought the other back, and met Eyrin’s skull with another blow. I fired. The bolt sliced through the mermaid’s tail as she continued to bludgeon Eyrin’s limp body.

The mermaid fell off but still held onto Eyrin’s hair. She struggled to pull herself upright.

“Eyrin!”

I sprinted towards them. She wasn’t moving. She couldn’t be . . . she was just unconscious. I had to take her away from the demon.

The mermaid looked at me, still clenching the bloodied rock in one hand and Eyrin’s hair in the other. Her red eyes gleamed. For a moment they faded into white—into human eyes—but then she smiled and her jagged teeth grew back, and she lunged at Eyrin like a striking cobra.

I froze, as though the air had turned to ice. My brain and my eyes disconnected—what I saw couldn’t be real. Nature couldn’t function this way. The monster I stared at, this half-formed human, couldn’t be ripping flesh off Eyrin’s body like a mountain lion on a deer. The chunks she swallowed whole couldn’t be pieces of flesh. The blood—she was covered. It stained her sallow flesh red.

This wasn’t happening.

I reloaded and aimed at the feasting demon, but before I could fire, a change beneath my feet threw me sideways. I landed hard on my hip, the crossbow flying out of my hands.

The deck tilted, sending loose items sliding towards the water; I lunged for the bow, desperate not to lose my weapon. It crashed into the railing and leaned dangerously against it, threatening to fall through.

Above, the great fore mast tilted towards the water as the ship careened. I should have been panicking but I still felt numb, the vision of Eyrin’s bloody corpse burned into my eyes, blinding me to everything else.

As the ship continued to lean, I lost control of my limbs and was suddenly face down on the deck, head smacking hard into a post. Still, I kept an eye on my crossbow. The tip of the black handle rested feebly against a railing, the ocean thrashing beneath it. I brought my knees up and pushed myself closer.

Whatever had been making the ship tilt, it released. I swiped for my crossbow and my fingers closed around it as we rocked back the other way. The deck levelled. I scrambled to get my feet under me.

Blacktail appeared beside me, her bloodstained hands void of a weapon. She crouched, bracing herself. The entire ship shuddered. It lifted on its side again, this time tilting the other way. Something other than the waves was at play.

The ship lurched and I nearly went down again, but I leapt forwards and grabbed the railing. Blacktail did the same.

Below our slipping feet, the mainsail drew dangerously close to the water. The deck was nearly vertical.

“They’ve cornered a whale,” said Blacktail.

Her eyes were enormous, her breathing fast and panicky. She had a white-knuckled grip on the railing.

Between fits of swinging my legs to get a hold on something, I managed to choke out, “What d’you mean?”

“I saw a few of them. They’re using harpoons. They cornered a whale against the keel. They jab at it, so it has nowhere to go but further into the ship.”

Below us, the masts drew almost parallel with the water. A swarm of demons clung to them like leeches, trying to weigh them down.

“They’ll capsize us!”

The saw-whet owl flag was half-submerged. The mermaids hung off it, tearing at it with their teeth and webbed fingers. The rope holding it to the mast seemed as feeble as a thread. Then, like a shrivelled maple leaf in autumn, it plucked loose and fell into the water, taking several cackling mermaids with it.

“Meela,” said Blacktail. She was staring up at her hands. “I’m slipping.”

Her voice was so calm, she might as well have been commenting on the direction of the wind.

I looked down, trying to find something for us to rest our feet on.

“Let go,” I said. “Try and land on those crates.” I nodded to the other side of the deck.

“I’ll break my legs!”

But she didn’t need to worry, because the whale must have escaped, and the Bloodhound crashed back down to the sea. My stomach lurched at the free-fall.

We slammed into the water and a solid wave pounded down on us. I held onto the railing with all my strength to keep from getting washed away. My crossbow pushed painfully into my arms as the deluge swirled around us. My ears knew nothing but the hollow, rushing sound of a current.

The water swirled endlessly over us. My lungs begged for air, the muscles in my hands and arms trembled, and I wondered if the demons had capsized us after all. But then the hollow underwater sound shifted, deafening me with a noise like a rushing river.

I welcomed an enormous gulp of air into my lungs.

The ship rocked violently, threatening to overturn with each tilt.

Beside me, the railing was vacant. Blacktail was gone.

I cried out, searching across the way for her body. But I couldn’t see her. So many corpses littered the water it was as though we’d taken a wrong turn at the River Styx. I scanned the bodies frantically.

A head emerged from the red water, staring at the rocking ship. The demon’s eyes had faded to normal, her skin ivory white. Her gaze found mine, but when I reached for my crossbow, she submerged once more.

The screams and firing crossbows had been silenced.

Panting with fear, I glanced around. My legs shook too badly for me to stand up. My hands still clamped the railing. I couldn’t pry them away.

I tried to yell for Annith but my voice stuck in my throat.

“Meela,” said a voice close to my ear.

I started. Blacktail hung on the other side of the railing, clinging to the same one I was.

“Help me over,” she said, her arms visibly trembling. “My feet touch the water when the boat rocks.”

I scrambled to my knees and pulled myself to my feet, using the railing as support. I leaned over it and grabbed her under the arms.

“Have you got a foothold on something?” I said. My voice was weak and quiet.

“A bit.”

“Next time it rocks up, push with your legs.”

She grunted. The Bloodhound swayed, and her legs touched the water, and as it rocked back up I pulled as hard as I could. I heard her legs scrambling to push on anything they could find, and then I wrapped my arms around her waist and hauled her aboard.

We collapsed onto the deck, gasping. Both of us shook worse than ever—probably from the cold, as well.