The depth gauge on her wrist ticked past 170 meters, and Cassia Venn let out a slow breath through the regulator, watching the bubbles spiral upward into nothing.
She hung suspended in the throat of Old Kowloon-9's drowned sublevel. The pressure rig hissed at her shoulder seals, a thin metallic complaint that burrowed into her teeth and stayed there. Green light from her helmet lamp knifed downward through seventeen stories of brine, illuminating nothing but drifting silt and the corroded spine of a pre-Severance cargo crane. Beyond the reach of her lamp, the water thickened into a black so absolute it pressed against her mask like a hand.
She had not told anyone where she was going.
Her boots hung three meters above the deck plating of what had once been a transit terminal. The dive line ran taut beside her, a yellow umbilical that surfaced somewhere far above in a section of the city still breathing air. Above the surface, Rhea would be pacing. Rhea always paced. Cassia imagined her boots clicking against the operations room floor in a slow metronome, the soft tap of her fingertips against the console where the dive telemetry scrolled. She had not asked for permission. She rarely did anymore. Permission came with questions, and questions came with people who wanted her to wait, and waiting was a thing she had stopped being able to do eleven days ago when Mira's transit tag had gone dark.
The water here tasted of salt and something older. Brine and the faint sweetness of long-decayed organic matter, the kind of sweetness that came from proteins broken down over decades. A faint metallic tang ghosted across her tongue from the recycled air in her regulator. Cassia pressed her mouth against the rubber bite. She did not swallow. She kept her breathing slow and even, four counts in, six counts out, the way the dive instructor had taught her in a training bay a lifetime ago.
The wreck lay where the survey drone had pinged it. Forty meters ahead, half-buried in a drift of silt that had once been the polished floor of a terminal concourse. The cargo drone's skull protruded from the muck like the rusted crown of some drowned monarch, sensor arrays folded against its chassis like broken fingers. Cables streamed from its underside in pale fronds, swaying in the slow current. Calcified tube worms had colonized the wheel housings, building small white cities of calcium across the undercarriage.
Cassia kicked forward. Her fin strokes were slow, deliberate. The suit held her body in a soft fist, and every kick cost her a fraction of air, but air was a problem she would solve on the way up. She had forty minutes in the main tank. Twenty in the reserve. Her arms were already cold inside the suit's thermal layer, the kind of cold that crept into the joints of the fingers and made them feel like old wire.
She had not packed a knife. A knife was two kilos she had not wanted to carry. She would remember that, later.
The drone was older than the Severance. She could read that in the way its plating had bloomed into orange rust, in the shapes of the access ports that no manufacturer still used, in the faded glyph of a shipping company that had not existed since before the Fold. Pre-collapse tech. The kind that still ran on protocols no one had bothered to update in over a century. Somewhere inside that skull was a data core. Somewhere inside that data core was the last ping from Mira's transit tag, recorded eleven days before her sister had stepped into the Pattern and not come back.
Cassia reached the drone and braced one glove against its flank. Rust flaked away under her fingers, drifting into the current like dead leaves in a slow wind. She could feel the vibration of distant machinery through the metal, the city's bones still groaning even this far below the waterline. Somewhere above her, the surface platforms flexed in the swell. Somewhere far above that, the sun was rising on a city that did not know she was down here.
She located the access panel on the drone's crown. Her multitool found the seam, and she began to work. The first bolt crumbled under the wrench. The second held. She leaned into it, feeling the strain in her shoulders, and the bolt turned with a soft complaint that traveled through the metal and into her glove.
The first eel came out of the dark at 173 meters.
It was a ribbon of copper-colored metal, three meters long, undulating through the water with the slow deliberation of something that had all the time in the world. Its mouth was a flat circle of teeth, gears and grinding plates designed for chewing through corroded wiring. A rust-metal eel. A scavenger that fed on dead circuits and the soft cabling of failed drones. Harmless to a person in a sealed rig, mostly. Unless they decided her air line looked interesting.
Cassia kept working. Her breath came in measured cycles. In. Out. The bubbles rose past her mask in pale ropes.
The second eel appeared from behind the drone's flank. Then a third, sliding out of the silt like something being born, their photoreceptors registering only heat and current. They did not attack. They circled. They watched.
She freed the panel. The last bolt turned to powder under her tool, and the plate swung open on a single surviving hinge, releasing a column of dark sediment that billowed out across her visor. She blinked it away. Inside the drone's skull, a confusion of wiring spilled out like the intestines of some long-dead animal. And there, at the center, a data core the size of her fist, caked in white corrosion but intact. A small indicator window on its side caught the green of her lamp and threw it back at her.
Cassia reached for it.
That was when the eels moved.
They did not attack her. They attacked her line.
She felt the tug through her harness before she saw them, a sudden sideways pull that snapped her head to the right. Three of them had wrapped around the yellow umbilical five meters above her, their gear-toothed mouths working at the rubberized sheath. The line frayed. A hiss escaped from somewhere inside it, faint but unmistakable, the sound of pressure leaking from the protected layers.
Cassia's hand closed around the data core and she wrenched it free from the wiring. The last of the connector pins snapped with a sound she felt through the suit more than heard. The core came loose in her palm, heavier than she expected, slick with corrosion. She shoved it into the chest pouch and slammed the pouch's seal with the heel of her glove.
Above her, the eels continued their work. The line frayed further. She could see the inner layers now, white threads beginning to part beneath the yellow sheath. Her throat tightened inside the collar of the suit. Forty meters of umbilical. Forty meters of line that was the only thing standing between her and a seventeen-story swim to the surface.
She kicked upward. Hard. The suit resisted her, water dragging at her limbs like wet cloth. She reached the eels in seconds that felt like minutes, bubbles streaming past her face in long white ribbons. Her gloved hand closed around the frayed section of the line above the worst of the damage, and she hauled herself hand over hand toward the surface, dragging the umbilical with her. The eels released the line and turned toward her, their flat mouths opening in synchronized curiosity.
She did not look at them. She kicked harder.
The regulator began to sound its low warning, a soft two-tone pulse in her ears. Twenty minutes of air left in the main tank. Her arms burned. The bubbles from her exhaust vent streamed past her mask. She could feel the data core's weight against her chest, pressing against her sternum with every breath.
She broke the surface at the corroded platform of a flooded transit station. The water here was only waist-deep, lapping against her visor as she crawled forward onto the deck grating. The line still trailed behind her, intact enough to mark her path back. The eels had not followed her into the shallows. They did not like the shallows. Too much noise. Too much light. She understood that about them now in a way she had not understood before.
Cassia lay on her back on the metal grating, chest heaving, the pressure rig sighing around her like something settling into sleep. The regulator settled into a slower rhythm. She unclipped the chest pouch and pulled out the data core. It sat in her palm, slick and salt-stained, a fist of old metal and older secrets. Her fingers trembled inside the gloves.
She pressed the activation stud on its side.
The core's indicator light flickered. Once. Twice. Then a soft amber glow steadied inside the small window. A faint crackle of static came through the external speaker clipped to her collar, and then a voice she had not heard in eleven days filled the space between her mask and her skull.
"Cassia. If you're hearing this, then the tag pinged. And you came looking."
Cassia's hand tightened around the core. The voice was younger than she remembered. Calmer than Mira had been in the weeks before she vanished. There was a pause on the recording, a long breath, and then:
"The Pattern isn't what they say it is. Listen to me. Don't follow me into the Fold without this..."
The recording cut to static. A long hiss of white noise filled the speaker.
Cassia sat up slowly, water streaming from her suit, the core's amber light pulsing in her palm like a small, patient heart. She had twenty minutes of air left in the main tank. She did not turn off the core. She held it against her chest and listened to the static, waiting for the next word.
The static did not come.
Somewhere above her, the city groaned, and the water rippled against the grating beneath her knees.
The climb took forty minutes. Cassia counted the rungs the way her mother used to count rosary beads, each one a small mercy, each one bringing her closer to dry air and the smell of something other than brine and rot. The core sat in the chest pouch against her sternum, and she could feel its weight through the wet fabric of her undersuit, a small gravity that pulled at her with every breath she took. Water dripped from the suit's cuffs and pooled in the hollow of her collarbones, and the recycled air of the service shaft tasted of copper and old plastic. Once, a maintenance drone passed her on the ladder, its optic blinking a polite green, and she did not look at it. She kept her eyes on the rungs above, on the small metal tags stamped with floor numbers, on the slow accumulation of distance between herself and the place where she had found the core.
The 142nd tier smelled like too many bodies and not enough ventilation. Cassia's hab was at the end of the corridor, third door from the service lift, a space no larger than a shipping container and twice as ugly. The door was painted a color the maintenance logs called seafoam but which was really just a pale, sickly green that showed every scuff. She keyed the lock with her thumb, and the door sighed open on a hinge that needed oil.
The hab was dark except for the standby glow of the wall unit, a thin strip of amber that traced the seam where the paneling met the ceiling. Cassia stepped inside and let the door whisper shut behind her. The room smelled the way it always smelled after she'd been gone more than a day: stale recycled air, the faint mineral tang of the water recycler, and underneath it the ghost of the jasmine tea she kept in a tin on the single shelf because the smell reminded her of their mother's kitchen on the 38th tier, back when kitchens still existed in the vertical sprawl.
She did not turn on the overhead. She knew the layout by heart. Four strides from the door to the narrow cot bolted against the bulkhead. Two strides to the left brought her to the utility console and its scratched faceplate. One stride to the right, past the small sink where the tap dripped every eleven seconds, brought her to the floor panel she had installed herself eighteen months ago, on a night when the weight of the case she was carrying felt like something that needed to be hidden even from herself.
Her boots left damp prints on the decking. She peeled the undersuit down to her waist and draped it over the chair that doubled as a desk, and the cold air of the hab raised the flesh along her arms into a fine pattern of goosebumps. The chest pouch she unclipped and held in her palm for a moment. The core sat inside it, no larger than her thumb, dense in a way that had nothing to do with its mass. She could feel the faint pulse of it against the whorls of her skin, that same slow rhythm she had felt in the cistern, though here in the dry air it was harder to be sure whether she was feeling it or imagining it.
The utility console woke when she pressed her thumb to its pad. The screen was scratched and yellowed, but it booted, and the inventory ledger loaded with a soft chime that was the closest thing her hab had to a welcome. She keyed in her operator credentials and waited for the system to accept them. It spat back the standard greeting.
Operator Venn, C. Log entry pending.
Cassia began to type.
She described the retrieval site by its grid reference. She described the core in field shorthand: composition unknown, resonance signature inconclusive, structural integrity nominal, no immediate hazard to handler. She described the water and the grating and the silence of the place. She did not describe the thing she had felt when the core first touched her palm, that sense of a door being opened somewhere behind her sternum, because there was no field shorthand for it and she did not trust her own hand to be honest about it at this hour.
At the bottom of the form, under classification, she paused.
There were three options. Anomalous biological, which would route the entry to the medical review board. Anomalous material, which would route it to the materials sciences desk and guarantee a follow-up site visit from people with clipboards and opinions. And then the third box, the one the system suggested for anything that did not fit, the one she had used twice before in her career and never without regret.
She checked the third box. She typed the single word she always typed when she checked it.
Unsinkable.
Then she deleted it.
She typed it again.
She deleted it again.
She stared at the blinking cursor in the empty field until the screen's dimming protocol kicked in and asked her if she was still there. She tapped it awake.
She typed: Unsinkable.
Then she deleted the whole classification line and replaced it with the word the system expected for objects that had no analytical value, the word that would route the entry to the salvage desk and let it rot there in a queue no one read.
Unsalvageable junk.
She saved the entry. The ledger chimed again, accepting the log. Somewhere in a server room three tiers above her, a piece of software noted that Operator Venn had retrieved an item of no interest and had done so at considerable personal inconvenience. The software did not care. The software had never cared about anything.
Cassia sat on the edge of the cot and looked at the chest pouch in her lap. The core was a small, dense thing, almost the color of bone, and she found that she did not want to hold it any longer than she had to. Not because it frightened her, though it did. Not because she did not trust her own classification of it, though she didn't. But because holding it made her feel like she was already halfway to a decision she had not yet agreed to make, and decisions like that were the kind that ended with people disappearing into report files and never coming back out.
She set the pouch on the floor beside the cot and reached for the panel.
The false floor was a square of decking she had pried up with a borrowed multitool and then refitted with small magnetic catches she had purchased from a vendor on the 97th tier who had not asked her name. Underneath it was a shallow cavity, maybe three centimeters deep, lined with a sheet of signal-dampening mesh she had cut from a decommissioned comms blanket. In that cavity she kept the things she could not file and could not discard.
A photograph in a plastic sleeve, edges curling. A lock of hair bound with a thread of silver. A handwritten note in their mother's looping script that said only, Come home when you can.
And beside those things, the spool.
The spool was small enough to fit in her palm, a matte black cylinder with a single recessed play button and a thin slot for a charging contact. There was no branding on it. There was no label. There was only a tiny adhesive dot on one end, yellowed with age, that she had placed there herself so that she could find the beginning of the recording without having to rewind through the silence at the start.
She lifted the spool out of the cavity and sat with it in both hands.
The last time she had played the message was seven weeks ago, in this same cot, in this same dark. She remembered that because it had been the night of a citywide brownout and the orbital mirrors had been the only light moving across the ceiling, and she had lain on her back with the spool held against her ear and watched those stripes drift past like the ribs of something enormous passing overhead.
She had promised herself, after that night, that she would not play it again until she had something to say back. She had broken that promise three times since, and each time she had felt the breaking of it like a bruise reopened.
She pressed the play button.
The recording began with the soft intake of breath that Mira always made when she was about to speak, the small preparatory sound of someone gathering their thoughts into a shape they could bear to deliver.
"Cass."
The voice was compressed, slightly metallic, warmed by the encoding in a way that made it sound closer than it was. It was Mira's voice and not Mira's voice. It was Mira's voice as it had been the last time Cassia had heard it, which had been over an unsecured channel on a night that smelled of ozone and wet concrete, before the channel had gone dark and the silence had begun.
"I don't have long. I know you can hear me, because if you couldn't, you wouldn't have made it this far into the file, and you always were the patient one. I need you to listen, and I need you to not come looking for me."
Cassia sat very still.
"I have seen something. I don't know how to say it properly. I have seen something that I think is not supposed to be seen, and I think the act of seeing it has already cost me more than I can calculate. I think the cost is going to keep being extracted. Do you understand what I'm saying? I'm not in trouble. I am the trouble."
A pause. The soft hiss of the recording medium.
"There's a place under the 11th tier where the water doesn't behave the way it should. There's a thing in that water. I touched it. I touched it, Cass, and I think it knew I was going to touch it, and I think it wanted me to. I want to be wrong about that. I want to be wrong about all of it."
Another pause. Longer this time.
"I am going to go back. I have to go back, because if I don't, the thing I saw is going to keep being a thing, and the people who are supposed to know about these things are going to keep not knowing, and the cost is going to keep being paid by someone who isn't me. I think that's how it works. I think the cost is always paid by someone who isn't the person who can afford it."
A breath.
"Don't come looking for me. If you come looking for me, you will find what I found, and you will do what I did, and then there will be two of us gone, and that is not a math problem I am willing to leave behind. Promise me. Promise me, Cass."
The recording ended. It did not end with a click or a tone. It ended the way a breath ends, with the soft cessation of effort, and then there was only the silence of the room and the drip of the tap and the distant hum of the building's recycler cycling through its long night.
Cassia pressed the stop button. The spool went quiet.
She sat for a long time with it in her lap. She did not cry. She had not cried about Mira in eleven weeks, which was a personal record she had not expected to set. She had decided, somewhere around the third week, that the tears were a form of expenditure she could no longer afford, because the act of recording her own grief in saline was beginning to feel like a confession she did not want to make to the empty air of her own hab.
She placed the spool back in the cavity, beside the photograph and the lock of hair and the note. She picked up the chest pouch. She placed it next to the spool. She looked at the two objects side by side for a moment. Her sister's voice and the thing her sister had touched.
She fitted the panel back into place. The magnetic catches clicked softly, one by one, and the floor was whole again, and there was no evidence of anything beneath it.
Cassia stood. She crossed to the small sink and drank a palmful of water that tasted faintly of the recycler's minerals. She did not eat. She had eaten twice today, which was more than usual, and the thought of food made the inside of her jaw ache.
She pulled the cot's single blanket down and lay on her back without undressing further. The blanket smelled of herself and of the faint, dry chemical tang of the cleaning agent the hab service used on the linens. She folded her hands over her sternum.
Above her, through the small translucent panel that served as a window, the underside of the smog ceiling was visible. It was the color of a bruise, orange at the edges and darker at the center where the city's thermal output collected in the upper layers. The orbital mirrors were somewhere above that ceiling, far above, and their light came through in stripes, narrow bands that moved across the cloudscape in slow, regular sweeps as the mirror array tracked the sun across a sky no one in the vertical sprawl would ever see directly.
The first stripe passed. Then the dark. Then the second stripe, slightly wider. Then the dark.
Cassia watched them the way she had watched them as a child from the window of their mother's hab, when the mirrors had still been a novelty and the vertical sprawl had still been advertised in the feeds as a marvel of human cooperation rather than a slow, vertical drowning. She had watched them then with Mira beside her, the two of them lying head to foot on the narrow bed, counting the stripes and arguing about what color the dark between them really was.
The third stripe passed. The dark returned.
Her eyes were open. Her eyes were closed. She was not entirely sure of the order.
The fourth stripe passed, and somewhere beneath the floor panel the core and the spool lay side by side in their shallow nest, and above the ceiling the mirrors kept their long vigil, and below the 11th tier the water waited, and somewhere in the city's data vaults the entry Unsinkable sat in a deleted line of a log file, and the entry Unsalvageable junk sat in the line above it, and the system had already forgotten both.
Cassia slept.
The rainstripes moved across her ceiling in their slow procession, and the hab breathed its small breath around her, and the dark between the stripes was, she decided in the last flicker of her waking mind, the color of her sister's voice, which was the color of a question she had not yet been brave enough to answer.