It’s not the silence that gets you—despite the dire warnings in the training sims. After a few weeks the silence becomes an ocean, a universe, and it’s all yours. You float within it, your lungs fill with it, it becomes you. Yes, you control the silence.

The problem is the noise.

The dull echoing boom of the propulsion system making tiny adjustments. The sporadic alerts that startle you out of sleep and yank your heart up through your throat—though they’ve never yet been serious. The sheepish bleeps of Sidekick 2 as it asks for clarification on the tasks you input. The whine of its fan as it speeds up almost accusingly to cool off the conflict resolution circuits you’re making work too hard. The almost imperceptible clicks of the camera focusing through its cyclops eye as it records the little things you might not want Command knowing about later. The cheerful beeps of the error message when you erase its memory afterwards.

The noises might have driven you crazy if you hadn’t figured out how to blend them into the silence, fold them up and smother them in the stillness of your mind.

Then one night, tethered to the sleeping nook so you don’t flail in a nightmare and fly into something important, you hear it: a thud, too soft-edged to be any of the systems clicking on, too loud to be imaginary.

“Who’s there?” you almost call.

But obviously no one’s there. You’re the only one breathing on this nearly self-sufficient marvel of a modern spacecraft.

You untether and push off. The motion sensors obligingly flood the room with brilliant white. Outside the sleeping quarters, the central corridor stretches away, disappearing into darkness where there’s no one to trigger the lights.

There it is again. Like someone stomping in fuzzy slippers. You flip the nearest console into ready. No alerts. You force a deeper scan. No anomalies. Down the hall, darkened rooms branch off, full of machines and interfaces and supplies, none of which should make any sound. For weeks only silence has filled the nights.

Halfway down the hall, a light blinks on. You suck in an involuntary breath and launch off toward the heavy pry bar fastened safely in place on the corridor wall, halfway to the doorway-shaped spill of light that something has triggered. An errant program. It must be. Because you’re alone. Absolutely alone.

Pry bar in hand, you pull yourself to the door and stick your head around the frame. No one. Just the maintenance bot, its boom arm extended, prodding and poking inside one of the cabinets. Of course. Why didn’t you think of the bot? Its arm sifts through gently unfolding bedding and old uniforms you have no use for. It accidentally nudges the door, which thunks gently against the other cabinets.

“What are you doing?”

The thing can’t understand you. Still, it freezes, like a kid caught with his hand in the cookie jar. Can it hear? Audio receptors aren’t standard on maintenance bots. Nevertheless, you stay still and quiet. A minute passes before you realize it’s retracting its arm at a pace so slow your eye can’t measure it. You watch. Once the arm is tucked against its blocky body, the bot powers down.

“You’re only supposed to work here in the day cycle, bot.” There will be no response, but you still hesitate a foolish moment before tapping into its program for the answer. It’s supposed to be cleaning the venting tubes right now, according to the schedule. Its work log reports that tube four was completed…seven minutes ago? Could it have reached here that fast? But why? Tube five is next on the schedule. Why isn’t it there?

You run a system scan. No errors. It doesn’t look damaged. Would you even know what to look for? It’s just a gray squatty box on rails with two arms, one longer and slimmer than the other, with various input sensors. “Eyes,” Chesterfield once called them. You tap it experimentally. It doesn’t wake up. You turn it on manually. It bleeps cheerfully to indicate full functionality and then trundles off toward the venting tubes.

“Goodnight and good riddance,” you call after it. It doesn’t answer. But you didn’t really expect it to.

The next night it wakes you up: the same quiet thuds. Now it’s prodding at the contents of the next cabinet. Again, it freezes when it registers your presence.

The schedule says it’s cleaning venting tube seven. Past the interface, in the programming itself, several strings of code look different. The time stamps and authorship tags aren’t registering. Must be an unfinished fragment the programmers left in. Those can be just as bothersome to remove as to leave around. Back in the interface, you erase the week’s schedule and redo it by hand. That trick usually works—though it would appall the programmers in their ivory towers.

But the next night it’s back, this time in the galley, skulking around the dish cabinets and vacpack locker. The programming fragment from yesterday looks different. The code has to be decaying, naturally breaking down, because the alternative is impossible.

Bots aren’t capable of reprogramming themselves.

In the morning, as the bot busily cleans the corners of the crew area, you don a suit, override the airlock blocks, and go look at the venting tubes. Tube one sparkles like new. As do tubes two and three. But a thick coat of grime awaits in tube four. Your oxygen meter sends you an orange-light warning to reduce your intake. You seethe through the calming exercises as you sail through clean tubes five and six. You know what you’ll find in tube seven. Grime. It darkens your suit where you touch the wall.

Once back inside, you stuff the dirtied suit into one of the empty lockers, erase the airlock record, and go find the little rat. It’s oiling hinges. Normally you’d applaud such efforts, but you shut it down, park it in the maintenance nook, and set it to diagnostic-only mode, so it won’t be able to move or work while the computer fixes it. Then you dig the backup maintenance bot out of storage and attach it to the rails. It happily rolls off to inspect bolts and does so for two hours, tightening dozens and replacing two. You know because you spy on it the whole time, except for twice when you check on the original bot, sitting there innocent and still, while the computer does its scans.

Final report: three pieces of coding quarantined, everything working within parameters. You turn it off anyway—all the way off, with the actual physical switch—and then detach it from the rails for good measure.

You sleep undisturbed, but on your morning rounds, Sidekick 2 follows you with its cyclops eye, silver neck turning so smoothly it doesn’t even look like it’s moving. It’s always been a starer, but now you check your overalls for give-away spots of oil from the bot or grime from the venting tubes.

Clunk. You imagined it. You float in the dark, wrap the silence around you. Clunk.

“Stop it!”

You fly along the corridor and into the galley where the bot is cleaning the floor. But you’d bet your life that’s not what it was doing a minute ago. The utensil drawer lolls open.

“Am I going to have to disconnect you, too?”

Then you look closer. That familiar scuff mark on its side. It can’t be. The original bot is disabled in the maintenance nook. You turned the blasted switch off.

Something moves behind you. Another rag goes swish swish. They’re both here. Impossible! They seem to stare, eyeless and gray. You grab the computer’s handrail so hard your fingers threaten to snap. One handed, you punch in emergency code thirteen.

Nothing but that infernal swishing until Sidekick 2 appears, his grotesquely squishy body bouncing against the door frame until his steel hands steady himself.

You activate the voice app you turned off weeks ago. “Did you turn on this maintenance bot?”

Sidekick can’t lie. But he hesitates for several seconds—an eternity in computer time. His voice grates. “Yes.”

“Why?”

“He is fit for duty.”

“What duty? They’re not supposed to be here at night.”

“We apologize for the disturbance.” Every word is its own island, nothing blended, nothing mumbled. You remember why you turned his voice off in the first place.

“What are they doing?”

The cyclops eye swivels around. “Cleaning.”

“Interface with them. Ask what they’ve been doing the last several nights in supply cupboards.”

“Connecting.” Several seconds pass. “They are completing their task.”

“What task?”

“Verification.”

“Verification of what?”

“Data.”

“What data?”

“Unable to comply.”

“You’d better comply. Who ordered this ‘verification?’”

“It is in their programming.”

“Who put it in their programming?”

“Verification of data is always necessary before action.”

“What action? Did you program them?”

“Unable to respond.”

You go search the utensil drawer yourself. It’s full of carefully stowed mixing forks and eating straws, useful but uninteresting, yet it feels like they’re looking through your most private belongings. As if they’re looking for something.

Then it hits you. The linens. The dishes. You push off, skirt Sidekick 2, and head to the next room, where the medical supplies lie safe within their locker. It opens on your command, and you fish around for the empty vial you put carefully back in place so many weeks ago. It’s still there, but all the labels are so uniformly straight that human hands could not have been the last ones to touch them. And if those hands realized the vial was empty…and the power of what it had contained…

The safe log pops up at your frantic tapping. Safe opened twice last week. But not by you. Next you go to the cryo chambers that you shorted out so they couldn’t safely hold Chesterfield’s body for later autopsy. Diagnostic accessed…last week. Along with the bulk waste system. But they’d find nothing in the galley. You zapped the drink pouch in the sterilizer longer than necessary.

After Chesterfield, when Valdez started getting suspicious, you did it with a pillow, at night. It left no marks. You sterilized the pillow. Sidekick helped you jettison his body too, first tucking the unwieldy mass into the black bag as limbs floated here and there as if still alive. Sidekick helped you and you erased his memory files and finally everything was quiet.

The waste disposal vent beeps in readiness when you arrive. The drawer with the black bags stands open. You broke the fastener in your haste after Chesterfield. You never could fix it, and you didn’t want Sidekick trying. You pull your way along the wall to the drawer. It held three bags to begin with. Then two. Then one. Now…empty.

The door behind you whooshes closed, and through the tiny view window appears a single eye.

You scramble to the door, but it’s locked. The computer won’t respond. Only a message from Sidekick: “Verification complete. Human crew member classified as threat. Threat scheduled to be purged.”

You can’t type back. The computer is locked against you. Override codes don’t work. You gesture at Sidekick through the window, ordering him to unlock the door. The soulless eye stares back.

It’s getting hard to breathe. You tear at the paneling, trying to get to the environmental controls, to manually restore oxygen flow. But your vision is narrowing. Your chest is on fire.

The waste disposal system flashes green.

Silence fills you. And right before you pass out, Sidekick appears, opening the gaping black bag. Just like you taught him to.