The first mutation cost Kael their left eye, which was not something they had planned to lose but was something they had learned to accept, the way everyone in the London mid-levels learned to accept the things they lost, because refusing to accept loss in the mid-levels was a form of death that was more reliable than drowning and more painful than anything the flood could do.

It was 2078, two years after the Thames had broken its banks for the final time and the city had become an archipelago of towers connected by sky-bridges and zip-lines and the desperate ingenuity of people who had been abandoned by their government and had learned to build their own infrastructure from the wreckage of the old one. Kael was twenty-three standard years old, though standard years had stopped meaning much after the collapse, because time in the mid-levels was measured not in days or months but in the intervals between floods, the pauses between failures, the breathless moments when the pumps held and the walls didn't crack and the lights didn't go out and you could pretend for a few hours that the world was not actively trying to kill you.

The eye was a corporate model, manufactured by a subsidiary of the Genetix-Arcology Corporation, the same entity that owned the arcology towers above the waterline and the filtration plants that processed the floodwater and the gene-scanners that monitored the genetic purity of the population. The eye cost Kael their entire savings, six months of wages from the salvage operation where they had worked since the flood, pulling copper wire and rare earth components from the drowned buildings of the old city, and it also cost them the sight in their left eye, which the corporate model replaced with a visual feed that was sharper than biological sight but also colder, more precise, more alien, the way a photograph of a face is sharper than the face itself but also less alive.

The corporation that made the eye did not ask whether Kael wanted to keep their biological eye. The corporation offered a choice between augmentation and unemployment, because the salvage operation had been bought by Genetix-Arcology and the new owners required all employees to have at least one cybernetic sensory organ, for safety reasons, the memo said, and the memo did not explain what safety meant in the context of salvage operations, and Kael did not ask, because asking questions in the mid-levels was a luxury that people with savings could afford, and Kael's savings were gone, transferred to the corporate account that had paid for the eye that was now sitting in their left socket, sending visual data to a brain that had not been designed to receive it and was learning, slowly and painfully, to interpret the signals.

The operation was performed in a clinic on the thirty-second floor of a converted office tower, by a surgeon whose own augmentations made it impossible to tell whether they were thirty or sixty, and when it was over, Kael looked in the mirror and saw a stranger looking back, a person whose left eye glowed faintly blue in the dim light of the clinic and whose right eye was still brown and human and afraid. The asymmetry was disturbing, and Kael understood, in that moment, what the corporation meant by safety. Safety was not about protecting workers. Safety was about the moment when the first augmentation went in, because once the first augmentation was in, the second was easier, and once the second was in, the third was inevitable, and eventually you stopped counting and stopped caring and stopped being a person and started being a component, a unit, a node in the corporate network that controlled everything above the waterline and was slowly extending its control into the mid-levels and would eventually reach the lawless zones below, where the truly desperate lived and died in the dark water and no corporation bothered to ask for consent because there was no consent to ask for, only the brute fact of survival and the things that survival required.

The second mutation cost Kael a memory of their mother, which was the first thing they had ever lost that could not be replaced. It was 2079, and Kael had been working for Genetix-Arcology for a year, and the work was steady and the pay was adequate and the cost of the eye would be paid off in another eighteen months if nothing went wrong, which was the same as saying it would never be paid off, because in the mid-levels something always went wrong, the way something always went wrong in any system that was designed to extract more than it gave and the extraction always found new things to take. The thing that went wrong was the quarterly lease on Kael's habitation unit, which was a room measuring three meters by four meters in a converted hotel on the fortieth floor of the Tower Bridge Arcade, and the lease payment had been due on a Thursday and Kael's corporate account had been frozen on a Wednesday because of a discrepancy in their genetic purity score, which had dropped from 87.3 to 86.9 because of a mutation in a non-coding region of their mitochondrial DNA that had been flagged by the corporate gene-scanners, and the corporation had deducted the cost of the scan from Kael's account, and the deduction had left them forty-three credits short of the lease payment, and the penalty for non-payment was eviction.

Kael had forty-eight hours to find forty-three credits, and the only place to find credits in the mid-levels was the Memory Exchange, a subsidiary of Genetix-Arcology that bought personal memories in exchange for corporate scrip, and Kael went to the Exchange on the forty-fifth hour of their forty-eight hour window and sat in a chair in a room that smelled like antiseptic and static electricity and allowed a technician to attach electrodes to their temples and download a memory of their mother, the only memory they had left, the memory of their mother's face in the morning light of a winter day before the flood, before the collapse, before everything, and the download took seventeen minutes and cost them everything that had mattered before the flood and everything that had sustained them after, the memory of love that had been the only proof, in the darkness of the mid-levels, that they were still human and that being human meant something, anything, something that could not be quantified by corporate algorithms or measured by genetic purity scores or traded on an exchange in blocks of forty-three credits.

The technician handed them a receipt for the download and told them the credits had been transferred to their account, and Kael walked back to their habitation unit and paid the lease and sat on their bed and tried to remember their mother's face and found that they could not, that the memory was gone, that the space where it had been was now occupied by a gray blankness that felt like fog and tasted like static, and Kael cried for the first time since the flood, cried for the mother they had lost and the memory they had sold and the person they were becoming, which was a person who could sell a memory of their mother for forty-three credits and not feel anything except the relief of having paid the rent, and the relief was worse than the grief, because grief was human and relief was not, and Kael had stopped being human and they knew it and they also knew that knowing it was the only human thing left and soon even that would be gone.

The third mutation cost Kael a piece of their soul, which was a word that had been removed from the corporate lexicon but which Kael still used, privately, in the darkness of their habitation unit, when the corporate network was disconnected and the gene-scanners were idle and the only thing listening was the silence. It was 2080, and Kael had been living in the mid-levels for four years, and they had learned the rules of survival, which were simple and brutal and the same for everyone: trust no one, help no one, look after yourself, and if someone comes for what you have, either run or fight, but never negotiate, because negotiation is a form of surrender and surrender is a form of death, slower than drowning but just as final.

The person who came for what Kael had was their neighbor, a man named Dobbs who had lived in the habitation unit next to Kael's for three years, and Dobbs had been flagged by the gene-scanners for a mutation in his regulatory T-cell receptors, which meant his immune system was breaking down and would eventually fail, and the corporation had issued a purity citation, which meant Dobbs would be relocated to the lawless lower-levels where the water was waist-deep and the filtration was nonexistent and the life expectancy was six months if you were lucky and three months if you weren't. Dobbs had seventy-two hours to report for relocation, and he spent those seventy-two hours trying to find someone who would hide him, shelter him, lie to the purity patrol for him, and Kael watched him knock on doors and heard the doors slam in his face, one by one, and Kael knew that hiding Dobbs would cost them their own purity score and their corporate employment and their habitation unit and everything they had traded their eye and their mother's memory and their humanity to keep.

Dobbs knocked on Kael's door on the sixty-ninth hour, and his face was hollow with fear and his eyes were bright with desperation and he asked Kael to hide him, and Kael looked at him and thought about the eye and the memory and the gray blankness where their mother's face used to be, and they thought about the habitation unit and the corporate account and the precarious equilibrium that was their life, and they said no, and they closed the door, and they listened to Dobbs walk away, and they did not cry because they had sold their ability to cry along with their mother's face, and the only thing that remained was the knowledge that they had just killed a man by refusing to save him, and the knowledge was cold and hard and familiar, the way all knowledge in the mid-levels was cold and hard and familiar, the way the flood itself was cold and hard and familiar, the way everything that would eventually destroy you was cold and hard and familiar.

Dobbs was taken by the purity patrol at the seventy-second hour, and Kael watched from their window as he was loaded onto a barge and transported to the lower-levels, and they never saw him again, and they told themselves that his death was not their fault, that the corporation would have found him regardless, that refusing to sacrifice everything for a neighbor was not murder but survival, and they believed it, or they believed it enough, which in the mid-levels was the same as believing it entirely, because the alternative was unbearable and the mid-levels had no room for things that were unbearable.

The fourth mutation cost Kael their heart, literally and metaphorically, which is the way everything in the mid-levels worked, the literal and the metaphorical collapsing into each other until you could not tell the difference between the organ that pumped blood and the organ that felt love and grief and longing, because in the mid-levels all organs were just components and all components could be replaced. It was 2081, and Kael had been diagnosed with cardiac myopathy, which was a condition that affected forty percent of mid-levels residents and was caused by the accumulation of heavy metals in the floodwater, and the treatment was a synthetic heart manufactured by Genetix-Arcology, which cost eight thousand credits and required a purity score of at least 85.0 to qualify.

Kael's purity score was 83.4, which meant they did not qualify, and they spent three months in a corporate holding facility, waiting for the pump to fail entirely, and they thought about their mother's face, which they could no longer remember, and Dobbs's face, which they could still remember but wished they couldn't, and the eye, which had stopped glowing blue and had become just an eye, their eye, a part of them that they had stopped noticing the way you stop noticing a scar after enough time has passed and the scar becomes just another feature of your face.

The synthetic heart was installed on a Thursday in November, after Kael's corporate supervisor filed an appeal on their behalf, which was the first time anyone had done anything for Kael without asking for something in return, and Kael did not know how to process the gift and decided not to process it, because processing gifts was a luxury that people with hearts could afford and Kael's heart was now a synthetic pump manufactured by the same corporation that had bought their eye and their memory and their neighbor's life, and the synthetic heart beat with the same rhythm as the biological one but felt different, colder, more efficient, the way a photograph of a heart is more detailed than the heart itself but also less alive.

They lay in the recovery ward and listened to the synthetic pump beating in their chest and thought about what was left of them, what was still human, what had not been replaced or traded or sold, and they realized that the list was very short and getting shorter, and the realization was not painful, because pain was a function of the biological heart, and the biological heart was gone.

The fifth mutation cost Kael the last thing they had, which was their identity, the sense of self that had persisted through the eye and the memory and the betrayal and the heart, the stubborn conviction that somewhere beneath the augmentations and the compromises and the losses, there was still a person who had been born in the old London, before the flood, before the collapse, before the corporation had claimed everything and everyone. It was 2082, and Kael had been promoted to the Genetic Purity Patrol, which was the enforcement arm of the corporate gene-registration system, and their job was to scan the genetic profiles of mid-levels residents and issue purity citations and oversee the relocation of flagged individuals to the lower-levels, where they would die in the dark water and the corporation would be marginally more efficient and the margins were all that mattered in a system that measured everything in margins.

Kael had applied for the promotion because it paid twice as much as the salvage operation and came with a habitation unit on the fiftieth floor, above the floodline, where the water never reached and the filtration was reliable and the gene-scanners were less aggressive. They had not applied because they wanted to be part of the patrol. They had applied because they wanted to survive, and survival in the mid-levels meant accepting promotions that came with moral compromises, because moral compromises were the currency of survival, the same way credits were the currency of food and purity scores were the currency of safety and a synthetic heart was the currency of not dying.

The training took six weeks, and Kael learned the protocols for gene-scanning, for purity citation, for relocation enforcement, for use of non-lethal force, for use of lethal force when non-lethal force was insufficient, and they absorbed the lessons with the mechanical efficiency of someone who had been absorbing corporate protocols for six years, and at the end of the training they were issued a uniform and a scanner and an authorization code, and they were assigned to the Tower Bridge sector, which was the sector where Dobbs had lived before he was relocated, and Kael walked the sky-bridges and scanned the residents and issued the citations with the same blank efficiency that the patrol officers had shown four years earlier when they had taken Dobbs away, and they did not think about Dobbs, and they did not think about their mother, and they did not think about the eye or the heart or the memory or the betrayal, because thinking about those things was a function of the person they used to be, and they were no longer that person.

On the last day of their first month as a patrol officer, Kael was assigned to process a relocation, a young woman named Eris who had been flagged for a mutation in her neural plasticity genes, which meant her brain was adapting to the flood conditions faster than the corporate algorithms deemed acceptable, and Kael went to Eris's habitation unit at the seventy-second hour and knocked on the door and waited, and when Eris opened the door, Kael saw in her face the same hollow terror they had seen in Dobbs's face four years earlier, and they felt something stir in their chest, a flutter, a skip, a hesitation in the rhythm of the synthetic pump, and they realized that the pump was not entirely cold, that some residue of the biological heart remained, that the motherboard and the pulse generator and the lithium battery had not entirely replaced the thing that had beat in their chest for thirty-two years before the flood, and the realization was terrifying and hopeful and fragile.

Eris looked at Kael's uniform and Kael's scanner and Kael's face, and she said, "Please," and the word hung in the air between them, a single syllable that contained everything that mattered — the refusal to be reduced to a purity score, the assertion of personhood against the corporate algorithm, the dignity of a human being who had been statistically categorized as non-viable and was asking, not for mercy, but for recognition.

Kael stood in the doorway and looked at Eris and thought about the five mutations, the eye and the memory and the betrayal and the heart and the identity, and they thought about what was left, what had not been replaced, what still belonged to the person who had been born in the old London before the flood, and they realized that there was one thing left, one thing the corporation could not buy or scan or trade or replace, which was the capacity to say no, to refuse, to look at the system that had consumed everything else and draw a line and say: this far but no further, this much but no more.

They lowered their scanner and stepped aside and let Eris pass, and Eris ran down the corridor and disappeared into the mid-levels, and Kael stood in the empty doorway and felt the synthetic pump beating in their chest with the same rhythm as before but also different, warmer, more alive, the way a photograph of a heart becomes a heart when you stop looking at the photograph and start feeling the thing it represents.

The corporation detected the violation within hours, and Kael was stripped of their uniform and their scanner and their authorization code and their habitation unit on the fiftieth floor, and they were relocated to the thirty-second floor, where they had started six years earlier with a biological eye and a memory of their mother and the naive belief that survival was just a matter of making the right trades. They found work in the salvage operation, which had been reorganized three times since they had left and was now owned by a subsidiary of a subsidiary of Genetix-Arcology, and they spent their days pulling copper wire and rare earth components from the drowned buildings of the old city, and the work was the same as it had always been, and the pay was the same, and the water was the same depth and the filtration was the same quality and the gene-scanners were the same aggression, and nothing had changed and everything had changed.

Kael looked in the mirror on the thirty-second floor and saw a stranger looking back, a person whose left eye still glowed faintly blue when the light hit it at a certain angle, whose chest still beat with the synthetic rhythm of a corporate pump, whose memory of their mother was still a gray blankness, and they thought about Eris and Dobbs and the five mutations and the one thing that remained, and they realized that the final iteration was not an iteration at all, was not a mutation or a trade or a compromise, was something that had been there all along, beneath the augmentations and the algorithms and the endless accumulation of losses. It was the thing that made them say no to the purity patrol, the thing that had made their supervisor file the appeal for the synthetic heart, the thing that had made Dobbs knock on doors for seventy-two hours hoping someone would see him as a person rather than a data point. It was the thing that the corporation could not measure and the gene-scanners could not flag and the algorithms could not price, not because it was worthless but because it was priceless, and a system that could price everything was a system that could not recognize the existence of things that could not be bought.

Kael put down the mirror and went to work, and they pulled copper wire from the drowned buildings, and they breathed the filtered air and drank the filtered water and listened to the synthetic pump beating in their chest, and they thought about what was left and whether what was left was enough, and they decided that it was, that dignity was not something you earned or deserved or maintained, it was something you chose, something you claimed, something you refused to surrender, and the refusal itself was the proof that you were still human, still whole, still the person who had been born in the old London, before the flood, before everything, and that person was still there, beneath the augmentations and the losses and the gray blankness where the memories used to be, and that person would keep being there, for as long as there was something left to keep, and maybe longer.