Mara is tying her hair back again, raking it into a topknot that tugs at her scalp. She’s been redoing it over and over, trying to calm herself, but her fingers are still shaking. She hopes her companion hasn’t noticed.

They’ve been lying in wait for a half hour, hunkered down in this crack in the basalt, under a sky that looks like a gaping black chasm. Mara has hardly ever been topside. Hardly ever leaves the habs. And she has never been out here in Slagland, where orbital bombardment left nothing behind but fused glass and cooled lava. The emptiness is terrifying, and she can’t help but imagine radiation seeping into her body, rotting her bones.

But she’ll do anything to get Io back—including hiring a half-savage scavenger. Mara sneaks another glance at the girl splayed out beside her. She has no hair to tie back; her head is shaved down to stubble. Circular gears are tattooed up the sides of her face, capping her sharp cheekbones, cobalt blue on sunless skin. Her clothes seem to be layers of grimy plastics, and when she walks it’s with a limp and occasional spasm.

She says her name is Scout, which is not a name. Mara knows someone like Scout would never be allowed inside her family’s hab or any other. Maybe that’s why Scout requested Mara’s chip as payment—maybe she thinks they’ll let her into a hab if she has a chip to scan. But having a chip is only part of it.

Mara watches while Scout checks their equipment: two silvery cloaks meant to hide them from airborne sensors, a small canister with wires sticking out one end, and powered cutters.

Mara knows what those are for, and looking at them makes her sick.

“You breathe real loudly,” Scout says, not looking up.

“Sorry,” Mara says, by reflex. She doesn’t say that it’s harder to breathe out here, that the air is thin and tastes like burnt metal in her mouth. She bought a filter mask for this specific reason, kept it hidden under her bed for a whole week. It’s still there. She only realized she’d forgotten it when she was halfway to the meeting point and it was too late to double back.

“You’ve never seen them before, have you?” Scout asks.

Mara shakes her head.

Scout looks at her, lips curled, sucking at the inside of her cheek. “You’re not going to like it,” she says flatly. She holds up one of the camfoil cloaks. “Take this one. Not as many holes.”

Mara takes it and pulls it on over her clothes. The material crackles, makes her arm hairs stand on end. It’s too big for her by half.

“The important thing is don’t freeze up,” Scout says. “Keep moving, and keep following me.”

“I’ll be fine,” Mara says, how she used to always insist to her parents, only half-believing it.

Scout’s mouth curls again, that expression Mara isn’t sure how to read, isn’t sure if it’s a smile or a sneer. “They’re here,” she says. “Look.”

Mara doesn’t know where to look, but then all of a sudden there’s an enormous black cube filling up the sky above them. No thunderclap, no sound at all, it just appears. A tremor runs through her whole body, and nausea hits her gut. Her ears are keening, her face is aching. There’s a rough staticky tongue licking her spinal column top to bottom.

The cube is like nothing she’s ever seen, an enormous black box composed of a thousand shifting slivers breaking and melding, rippling, almost liquid. Blinking red sensors swarm around its edges like flies. She can’t tell how close it is—one second it seems right on top of them, the next a mile away. Vertigo swamps her, and she retches.

“There, there,” Scout mutters.

Mara suspects sarcasm, but she’s too dizzy to be sure.

As she watches, an enormous oily black bubble forms on the underside of the cube, like water beading at the end of a nozzle, then falls. It splashes apart on the slag, revealing its cargo. Mara takes a sharp breath. It’s an old man, scarecrow-skinny, naked, with skin so pale it almost glows against the pebbly black rock.

But instead of a head, or perhaps enveloping it, there’s spiny black machinery, with a red sensor pulsing right where the old man’s face should be.

Mara squeezes her eyes shut for a second, fighting nausea. She knows it’s real, but it feels like a nightmare. When she opens her eyes, the old man is staggering to his feet. The liquid black remnants of his bubble pool together and climb up his naked body, then further, spiraling up into the sky as a single knarry tendril that hooks into the bottom of the cube.

The other end latches to the old man’s machine-mask, jerking him fully upright like a marionette, and Mara can’t hide her flinch.

“Now you’re not breathing at all,” Scout says in her ear. “Find a happy medium. Between the huffing-puffing and the not-breathing.”

Mara makes herself take a breath of the charred metal air as the other bubbles start to fall. They splash down one after another, bursting apart; the passengers wobble upright, and their cables wind skyward to connect them to the cube. There are dozens and dozens of them, and Mara searches for Io’s body. Her jutting ribs, her short thick legs. She wants to see her so badly, and at the same time she dreads it.

By the time the black rain stops falling, there are nearly fifty men and women and children shivering on the basalt. Then the cube moves, sliding soundlessly forward, sending a ripple through the black forest of tendrils, and all of them start to march.

Mara turns to Scout, trying to share the anguish, but Scout’s face is expressionless. She asks her question anyway, chopping the words out of a shaky breath:

“Why would they do this to us?”

Scout runs a pensive finger down her tattoos. “They might be bored,” she says. “You ready?”

Mara swallows. She’s never felt less ready for anything. She wants to be back in the habs, back in the safe white cocoon of her family’s house.

But Io is marching.

“Ready,” Mara says. “Yes.”

Scout leads the way out of the trench, camfoil cloak flapping behind her, and the hab girl follows good and close, keeping pace how she promised she could. Her name is Myra. Or Meera. Or something like that.

Scout is more concerned with her promised payment, the access chip nestled in the hab girl’s blue-veined wrist. A small fortune on the black market, and it can’t be taken by force. Hab folk are clever that way. Their bodies are all wired up with electricity that can fry the skin off your fingers if you touch them when they’re agitated. She already got a little burst of it when she brushed the hab girl’s elbow on accident.

So she has to do the job, first. She’d have preferred to leave her client underground—less factors, less fuck-ups—but she doesn’t trust herself to spot the right walker, since hab folk aren’t so much for tattoos or scars or looking interesting in general. Myra’s along for identification purposes.

“Start looking,” Scout orders. “But keep your head down as much as you can.”

The hab girl gives a grim-mouthed nod. They’re coming up on the walkers from the rear, and as they pass into the shadow of the cube the tug gets stronger. Oh, the tug. It’s like tiptoeing a fucking precipice whenever she gets near the thing. But she has to stay focused.

The walkers are slow. Partly because they’re barefoot, no boots or even gelwrap to protect them from the rock. Scout sees smashed toenails, flesh bruised blue and swollen underneath. Gooey red abrasions. Puffy ankles, pus-lined cuts. And the stink is awful. They’ve been pissing on themselves as they go, sweating sharp and sour.

Despite all that, every walker moves with the same plodding sleepwalking gait, never favoring their twisted ankles or pausing to clean a cut. Scout throws a glance back, to make sure the hab girl is still following. Her face is red and agitated but her eyes are dry, which is a good sign.

“I haven’t seen her yet,” the hab girl mutters. “At least. I don’t think I have. They all sort of... walk the same.”

“They do, yeah.” Scout casts an eye up at the sensor swarm. So far, so good: none of them seem to have noticed the cloaked interlopers. “They march all the way across the Slagland,” she adds on a whim, feeling oddly proud of the fact. “And all the way back.”

They’re in the thick of it now, weaving between bodies flecked with grime and gore. So many more of them than there were the first time she saw the cube. Scout recognizes a few by their skins and silhouettes.

“Left, left, left-right-left,” she chants softly. “How would you really get around like that? Stepping three in a row with the left, I mean. Makes no fucking sense at all.”

No reply from the hab girl, who is stumbling along behind her, head on a swivel, green eyes winched wide. She looks a bit dazed. Hopefully she’ll be sharp enough to recognize their target.

One of the sensors finally detaches itself from the others and drifts down toward them.

“Don’t move,” Scout hisses, dropping to her haunches. A walker trips over her; his tendril yanks him back to his feet with a sound of popping cartilage, and he circles around her. Scout makes herself as small as she can under the camfoil and is satisfied to see that the hab girl is doing the same thing beside her.

The sensor, an angular black shard around a glowing red optic, buzzes back and forth overtop of them for a moment. Then it’s gone, back to the cube, and Scout motions for them to move again. Her heart pounds happily in her chest. This is a game she’s played before, but it has an extra objective this time around, a new ending she’s never tried.

It only takes them a moment to catch up to the walkers again, slip back into their midst. They comb through them in columns, up and down, up and down. Scout finds herself envying their smooth dreamy walk: so unlike hers, which is all slouch and twitch. But she doesn’t envy the heavy vantablack masks clamped over their heads.

Behind her, Meera says something too quiet and choked up to hear.

“What’s that?” Scout asks, but she already knows from the way the hab girl is stopped and staring.

“That’s her,” she whispers. “That’s Io.”

Mara has seen Io naked before, when they were little children and they bathed together, and later when they were older and made a solemn agreement to show each other their breasts, but this time, for the first time, she feels a hot sick wave of shame.

Io’s skin, so beautiful only a week ago, is pitted with tiny scars from wind-hurled debris; grime is worked deep into her creases. The edge of her ribcage and the jut of her hipbone both look sharp enough to cut.

And where her face should be, where her fiery eyes and smile should be, there’s a metallic mass of spars and planes.

“You sure?” Scout says, darting a quick circle around Io, eyeing the cable that stretches up into the sky and shivers slightly as Io walks.

Mara nods, not trusting her voice.

She and Scout fall into step alongside her thralled friend, and it feels unreal. For a moment Mara imagines they are walking through the hydrogardens in her family’s hab, but Io would never be able to walk so silently. She always had something to be overjoyed or over-furious about.

“I’m going to fire up the cutters,” Scout says. “You’re going to hold her still.”

Mara feels panic bubbling up from the bottom of her, eating away at her muscle. It would be better if her and Io’s roles were reversed, if Io were here to save her instead. Io would be quicker and stronger and more determined and less afraid. But also, in a tiny cold corner of her mind, Mara isn’t sure Io would come.

She buries that thought deep.

“Here we go,” Scout says.

The cutters come to life with a shriek and a shower of sparks, one of which sizzles onto Io’s moving foot. Mara flinches. Io doesn’t. The cutters buck and vibrate in Scout’s grip. Mara remembers how Scout twitches sometimes, and she imagines the cutters accidentally shearing through Io’s flesh, lopping off her arms and leaving cauterized stumps.

She dives down onto the basalt and wraps herself around Io’s legs. Normal Io would laugh, if Mara did something like that. Laugh and ask what in the hell she was doing. This Io just stumbles forward and falls without making a sound.

The black cable stretches taut, and Scout lunges with the cutters. It’s loud, horribly loud; the metal teeth grind and scream against the cable. Mara screams too, for the pain flaring through her eardrums and jaw and for fear. Scout’s knee ends up jammed against the side of her face. Mara clamps even tighter around Io’s legs; the smell of scorched hair and skin fills her nose. She feels her heart slamming hard in her chest. The walkers are passing all around them.

Scout grunts something she can’t hear, and when Mara looks up at her, she sees the red sensor swarm descending, weaving through the forest of cables. The cable that matters, Io’s cable, is barely a thread now, writhing between the cutters’ blades. Mara watches Scout wrestle with it, willing her on, they’re close, so close...

The last shred of Io’s cable snaps, and Mara feels a jolt run through her friend’s entire body. Then Io is limp, dead weight in her arms, and Mara tries to pull the camfoil up to cover both of them from the approaching sensors. The black shards are sprouting arms now, claw-tipped, extending. One of them reaches Scout and she turns the cutters on it, slicing it in half, but then two more drop from behind her and wrest the tool out of her hands.

Mara has Io’s slack body crushed against her; there’s no way she can run. A sensor swoops down and grips at her cloak, peeling it off. She seizes the hem with her free hand, trying to tug it back. A straggler lurches into her from behind and she loses her grip on both the cloak and Io’s waist. The silvery camfoil ripples into the air, but in that instant Mara sees Scout brandish her last piece of equipment, the strange stubby tube.

The air seems to thicken, and all of a sudden the sensors freeze in midair. Scout gives a ragged shout of triumph and grabs her cutters back, fumbling them into her bag. She seizes Io under one arm, Mara takes the other, and they all three haul upright. Mara realizes it’s not only the sensors that have frozen: the walkers have stopped. The cube has stopped. For an instant she wonders if time itself has stopped.

“Pulse bomb,” Scout says. “It gets under their skin a bit.” She takes a look at Io. “She your girlfriend, then?”

Mara chokes on a laugh. “What?” She hardly cares. She’s on the edge of mania, full of giddy adrenaline. Nothing makes sense, but Io is free.

Then the walkers press in from all sides, flailing their emaciated arms, reaching with bony fingers. Mara doesn’t have the breath to scream, but Scout gives a shout of alarm. She ducks her head and together they bully through the crowd, dragging Io with them. Blows rain down from every direction, but the walkers are weak, frail. The few times they grab hold of Mara, she quickly tears free.

The assault lasts an instant and an eternity, then it’s over: Mara and Scout collapse on the basalt with Io between them, out of the shadow of the cube, out of reach. The walkers strain at their cables for only a moment before they turn back around.

“That’s new,” Scout pants. “Never seen them do that.”

Mara watches, slowly getting her lungs back, as the cube starts to move away. The men and women and children start to march again.

Scout, like always, is almost sorry to see the cube go. She feels the tug like a little hook behind her belly button until the cube and the walkers are almost over the horizon. She’s leading the hab girl and her friend, whose name is Io—easier to remember, like the two letters, I and O—in the opposite direction, toward a derelict downtube. She can touch Io without any hab-folk electricity scorching her, either because Io’s unconscious or because the cube turned it off somehow.

Scout can’t take them straight back to the Nexus, obviously. First they have to get the mask off Io’s head—Myra is real insistent on that point—and Scout needs to get her payment. So she’s taking them down into a little tunnel where she used to sleep sometimes when she was younger. Myra can’t even wrap her head around the idea.

“Is it shielded?” she keeps asking. “Is there air? Clean air?”

Of course, she’s more worried about Io. Scout can tell by how she won’t take her eyes off her. It makes her like the hab girl a little more, and makes her wonder what Io looks like under the black machinery.

Scout winches the tunnel hatch open a crack and tosses a rock through, to make sure it hasn’t been taken over in her absence. No surprised swearing or scurrying sounds, just a dull clang. Good sign. She opens it the rest of the way and leads them in, switching on her torch. The interior is more cramped than she remembers it, but of course she was smaller then, and only one person, not three. The nest of insulation she built is still intact. The air vent in the ceiling is still whispering away.

“Lovely little place,” she says, once they get Io laid out with her head cushioned. “Yeah?”

The hab girl gives a vague nod. “You live here? In the tunnels?”

“Not here,” Scout says. “I live in the shanty blocks deeper east from here. Tubetown.” She doesn’t like the hab girl’s pained look. “You hab folk live in the tunnels, too, you know. Except inside those pretty bubbles with those pretty lasers that slice the head off you if you’re not careful. If you get too close.”

The hab girl flushes. “I went to Tubetown once,” she says. “You know. On an excursion.”

“Fuck you,” Scout says, mostly just to see if Myra can flush any redder—she can.

“Sorry.”

“You’re very good at being sorry,” Scout admits. She decides to let her off easy, even if she is a rich stupid hab girl. It’s been a long day for someone who’s never even seen Slagland before. “Let’s get the mask off, now,” she says.

They flip Io onto her stomach, then Scout turns the cutters to what she assures is the lowest possible setting and sets to work. Mara crouches as close as she can, watching the buzzing teeth nibble their way through smooth black metal.

Now that Io is safe, she is realizing, more and more, how dangerous it is to be out here. She has no idea how this world works. She has no idea if Scout is trustworthy or not—they’re only together because Scout was the first person she found, as she wandered through the Nexus, who would agree to take her to the cube.

Mara’s family will know by now that she left the hab. They might already be searching for her, using drones and wearing safesuits. If they find her with Scout, they’ll probably think she was kidnapped.

“How do you know so much about the cube?” she asks, to distract herself. “About the visitors.”

Scout’s face is furrowed in concentration, illuminated orange by the smelting glow of the cutters. Mara realizes it might be best not to ask her any questions until the job is done, but Scout replies without taking her eyes off the cutters.

“They been around,” she says. “A couple years, at least. Longer. It’s just the cube comes more frequent now.” Scout blinks. “Got a bit of sweat coming for my eye. Wick it for me, will you? But don’t shock me.”

“Oh. Yes, okay.” Mara leans in and sees the bead of sweat trickling down from Scout’s forehead. The cutters are hot. She reaches awkwardly and thumbs the droplet away.

“Even before, there were stories,” Scout says. “Legends, I guess. People who said they got picked up by the big black box. But those people were usually fucked up on chemicals or head damage.”

“Our hab, we didn’t detect them until a month ago,” Mara says.

“Because you hab folk never poke your noses out of your little bubbles.”

Mara doesn’t try to argue that point. “They sent us something. We couldn’t understand it.”

She remembers the panic when the first incomprehensible swings in gravity and spikes in heat were detected by machines almost too old to trust. Not long after that, re-activated surveillance cams caught an image of the cube adrift in a toxic yellow sky. People got strange ideas. Judgment. Apocalypse.

In another hab, a band of younger members wanted to go topside to communicate with the visitors in person. Io decided to join them, even after Mara pleaded and pleaded with her not to.

“What do they want?” Mara finally asks.

Scout grunts, then switches the cutters off. “Ask Io, here,” she says. “She spoke to them last.” She reaches with her sooty fingers and pries the mask apart. Mara’s lungs catch. It doesn’t seem to want to leave; tiny black tendrils trail from the mask’s insides, still clinging at Io’s scalp. Her hair is greasy and knotted in clumps.

Mara helps Scout flip Io back over, and together they gently pull the front half of the mask away. More tendrils, this time clinging to Io’s cheekbones. When Mara plucks them off they leave tiny sucker marks behind. Io’s face is pale and sickly, but it’s Io’s face, and Mara feels relief wash over her like a wave.

It was all worth it. She’ll bring Io back to the hab, get the both of them through a radiation cleanse, and everything will go back to how it was but better. Because Io will be so grateful to her, and maybe put her head on her shoulder and cry sometimes, and need her. Mara would be alright with that.

Io’s eyes flick open; Mara’s heart surges in her chest. Io touches her face with her grimy hands, claws at the space over her head where the cable would be. Her eyes are panicked. They leap around the tunnel and land on Mara, who is just now putting a comforting hand on her friend’s bone-and-sinew arm.

“What did you do?” Io asks, in a horrified whisper. She jerks her arm away. “What did you do?”

And she starts to scream.

Eventually Io, who is beautiful under the mask but not in the way Scout imagined, wears herself out and collapses unconscious. Scout watches with mild interest as Mara—she’s sure of the name now; Io screamed it over and over, interspersed with curses—slowly shifts Io onto the insulation, turning her on her side. She is trembling. Red-faced. At the start she tried to reason with her friend, tried to soothe her, but eventually she gave up and bore the shouting and the pounding of small weak fists in silence.

Now Mara is running her fingertip along the sucker marks that score Io’s pallid face. She looks up, hollow-eyed, and Scout isn’t quick enough to look away.

“Your tattoos,” Mara says thickly. “You have scars under them. Right?”

“So I do,” Scout replies, feeling a little bad now, a little sheepish. Of course, there was no way she could have known that Io would be crazy when they unhooked her. That the tug would be so much stronger than the one Scout felt, and only felt around the cube.

“Why didn’t you tell me you used to be one of them?” Mara asks, in a way that suggests she will start crying soon.

“Never asked, did you?” Scout gives a rueful shrug. “The big black box got me about a year ago. I figure I marched for a month. Maybe more. Tough to tell. Time’s different when you’re with the cube.”

“I’m sorry.” Mara rubs her eyes. “Can you. Can you tell me what it was like?” Her eyes stray back to Io, who is breathing heavy and slow.

Scout prefers not to talk about it; there’s a reason she had the marks tattooed over. People get odd around you when they find out you were a walker. But she feels sorry for Mara, who is always sorry, so she puts her chin in her hand and thinks of how to describe it.

“When you’re up in the cube, you’re in this sort of cocoon,” she says. “It’s thick and black and warm. And you’re seeing things. Nonsense things. Like when you breathe too much fumes or take a bad hit of lucie.” She tries to recall specific images to mind. “This one I remember seeing a lot, it was like a hydrogarden. Except the plants are gigantic, and the stalks are red-brown. I mean gigantic, like, up up into the sky. And there’s a bright hot lamp up in the sky, too, and the colors are all topsy-turvy. The sky is blue.”

Mara wraps her arms around her knees and tips her ash-blonde head back against the tunnel wall. “What else?” she whispers.

“Little drones flying around,” Scout says. “But with odd rotors that pump up and down. Like this.” She mimics the motion, flapping her arms. “And they don’t really move like drones. They move jerky, like, skipping around in the air. And they sing.”

Mara looks surprised, then murmurs something she doesn’t quite catch.

Scout leans forward a bit. “Burns?”

Mara enunciates the word this time. “Birds.”

It’s only vaguely familiar. “Water, sometimes,” Scout continues. “I saw water. So much water it was like... You know the rock topside, with the ups and downs and slopes? Except made of water. Clean water, too. With wriggling things swimming in it.” She puts a finger to her temple and screws it back and forth. “Nonsensical shit. Pretty, though. A pretty trip.”

“What about when it sets you down?” Mara asks in a strangled voice. “When it sets you down to march?”

“It hurts.” Scout searches for words. She hasn’t talked much about the cube, even though she still likes to follow it sometimes, likes to see it and know it’s there. “You see how ugly it all is, compared to the cocoon dreams. You feel angry. But then as you walk, it gets better. I guess it feels like working a scab off. But more so.” She pauses, feeling slightly unbalanced. She’s said too much, and Mara is looking at her as if she’s the one who knows things, not Scout. “Like a pinch or a nice hard slap when you’re fucking,” she adds, to rejigger the power balance back and make Mara back off. “The good hurt.”

Like clockwork, Mara’s ears dye bright bright red. It doesn’t shut her up, though. “How did you get free? I mean, who cut you loose?”

“Nobody,” Scout says. “Just one day I’d had enough of it. So it let me go.” She’s had enough of the talking now, more than enough, and she’s ready to snap at Mara if she asks another question. But Mara doesn’t. Instead, she rolls up her sleeve, exposing her wrist.

“You can take my chip, now,” she says wearily. “You did your part. Of the deal, I mean. You freed her.”

Scout eyes the telltale blue glow of the subskin implant. “Could wait until we’re back in the Nexus, if you want,” she offers, surprising herself a bit. “Pick up a numbing gel. So you don’t feel it.”

“I’d rather just get it over with.”

“Sure,” Scout says, and retrieves the cutters, flipping out the utility nanoblade from the underside. “You have to turn off your sparkplugs, first. The defense mesh, or whatever.”

“It’s turned off,” Mara says, sounding almost hurt. “I turned it off a while back. So I wouldn’t shock you by accident.”

“Oh. Good.”

Scout has Mara lay her wrist out flat on her knee, then goes in with the cutters. It’s quick: slice-slice and the chip is carved out, and then she helps Mara put disinfectant on the cut and wrap it up. Her skin is smooth and warm and gives no shocks.

“What do you want it for?” Mara asks. “It won’t get you into the hab.” She looks embarrassed. “They scan other things, too. Your face. Your biometrics.”

“What makes you think I want to live in a bubble?” Scout wipes the bit of blood off the chip and peers at it. “I’m going to sell the thing. They use them to make pirateware. I’m going to sell it for a half milly and be the fucking queen of Tubetown. Maybe use the money to set up a supshop.”

She thought she would feel triumphant holding the chip in her hand, but Mara’s anxious face and Io asleep in the corner make it hard.

She tucks the chip into her boot. “We should sleep, too,” she says. “I’m fucking tired. I’ll take you both back to your hab in the morning. Hope they won’t be too pissed about you losing your hardware.”

Mara looks almost surprised, like she was expecting Scout to vanish as soon as she had the payment.

“Thanks, Scout,” she says, and it sounds kind of nice hearing her name in that swanky hab-folk accent. Scout grunts, then bunches the camfoil cloak up under her head as a pillow and shuts her eyes.

Mara is tired too, so tired she thinks that if she slips off to sleep, she might never wake up. Instead she sits beside Io and watches her breathe. The tiny cut on her own wrist seems to pulse against its bandage.

She is thinking about the cube. About the things Scout saw in her cocoon. They weren’t nonsense—Mara is sure of that. They were visions of the old world, the way it was before the oceans calcified and burned away, before the sky was smogged dark.

She learned about such things when she was a child. She knows that wars and contagions and famines and climate disasters decimated the population and drove the survivors underground. She knows the habs are descended from families who were wealthy and lucky enough, centuries ago, to find safety when the world collapsed around them.

She looks down at Io’s troubled face and remembers one of the things Io screamed at her. This was our fault. This was our fault. Not theirs, ours.

Mara unties her hair and lets her eyes flutter shut. She cradles her wrist, trying to understand why the cube would show Scout a world long gone. Trying to understand why the visitors had come at all. Her thoughts slip and slide into dreams.

When she opens her eyes again, the tunnel is dipped in a faint red glow. Mara checks on Io. Still sleeping, chest rising and falling. Scout is still snoring. She realizes the glow is coming from the corner, from the discarded half of the mask they cut away from Io’s face.

Mara hesitates for a moment, then shuffles upright. She crawls over to the angular black shard. Its red sensor has flared back to life, and one of the tiny black tendrils is waving back and forth. Mara has the sudden impression that it can see her. She grips the broken mask with both hands and lifts it up to her face, surprised by how light it is. The inside is impossibly dark.

What did Io see these last six days? What changed her? Mara takes a last glance at her friend, then puts her face into the mask’s black void.

She sees nothing. Feels foolish. Then the forgotten tendril snakes its way up to her temple and—

A beautiful whirlwind of images. The rolling oceans, a massive fish, no, a whale, leaping out of the water, tail thrashing, spray sparkling in the sunlight. The tall forests, the ancient trees teeming with brightly colored birds and gleaming insects.

She sees life everywhere, and she is not the only observer. As she drifts bodiless over lush green hills and rocky crags, over rushing rivers and waterfalls, the cube is drifting along with her through wide blue sky.

But it isn’t colored black. It shimmers and reflects the light, almost translucent. Mara can feel minds inside it; with sudden certainty she knows there are one hundred and seventeen of them. Simpler minds than hers, more elegant, made of reverberating crystal instead of flesh and salt and sparks. Machine minds with one insistent drive: spreading life. She can feel their joy at every new creature they see, especially at the smooth-skinned bipeds beginning to roam the grasslands.

Outside the mask, Mara’s hands start to tremble. She knows what’s coming next.

Inside the mask, she sees the cube depart, sailing through starry space, searching out new worlds where conditions can be optimized, where life can be seeded. They are gone for a thousand years. Ten thousand. But they do not forget the small blue planet.

They return to a wasteland. Mara feels their simple joy stripped away and replaced by thick dark grief. She feels their stark calculus, a near-consensus of one hundred and sixteen crystalline minds: this world is beyond saving. She feels their slow-building fury.

Mara yanks the mask away from her face. The tendril slucks free with a pop; a warm drop of blood flicks and splatters against the back of her hand. She realizes it had begun to burrow into her skin.

“It wasn’t our fault,” she whispers. “It was the ones before us. It wasn’t us.”

But even as she says it, she knows it was people like her. People like her in the pretty bubbles. That’s why Scout could leave the cube behind so much easier than Io. It wasn’t people like Scout who made the world collapse.

She stares at the red sensor and it stares back, unforgiving. Then she crawls back to where Io is sleeping and curls up beside her. She squeezes her eyes shut.

She understands, now. The visitors are punishing them. They want them to march across the slag, across the ruins, across everything they destroyed.

“Your friend left.”

Mara jerks awake. Scout is crouching by the tunnel entrance, putting her things in her rucksack. Mara’s heart thrums in her throat. She stares at the space Io’s sleeping body should have been occupying.

“Where?” she asks.

Scout doesn’t meet her eye. “It’s no good,” she says. “She’s got the tug. Stronger than I ever had it.”

Mara doesn’t reply. She stumbles to the entrance, past Scout, and seizes the ladder with trembling hands. She hauls herself up the rungs as fast as she can, ignoring the sway and creak. When she gets to the top, she can see Io limping into the distance. Beyond her, Mara sees the drifting black shape of the cube.

Io has her arms outstretched as she hobbles along, and Mara can hear her shouts half-swallowed by the emptiness. And now in her own belly, she can feel the tug drawing her in the same direction.

She starts to run. Maybe because she still loves Io, maybe just because she’s come too far and endured too much to let her go again. She gasps at the thin metal air, lungs straining, arms and legs flying. The black rock is uneven and twice she stumbles. She’s still faster than barefooted Io, far faster.

But she isn’t racing Io. She’s racing the cube, and the cube is winning. Its shadow slides towards Io like a razor across skin. Mara is panting, pushing. Every last shred of muscle in her legs is screaming. She trips on a crag in the basalt and splits her knee, shreds her palms.

No time to stop. She scrabbles back upright and reaches Io just as the cube’s shadow envelops them both. Her friend’s face is streaked with tears.

“It was our fault,” Io is babbling. “Our fault. Our fault.”

Mara tries to drag her away, but Io goes limp and heavy in her arms. The cube is directly overtop of them now; Mara’s spine is crackling with it, her ears are humming. The tug in her stomach is magnetic.

She knows she should leave Io and run. She knows their guilt won’t unscar the sky or replant the forests or bring back the oceans. But maybe nothing will. Maybe the visitors are in black because they have only come to mourn.

Then she remembers the calculus: one hundred and sixteen minds thought this world was beyond saving, but there had been one hundred and seventeen minds in total.

If the broken mask could show her the visitors’ thoughts, maybe there was a way to show them hers. Maybe there was a way to talk to the one in one hundred and seventeen who thought there was still a chance to reverse things, if not for her and Io and Scout then for the ones who would come after them.

Mara hopes so. She wraps her arms around Io as black rain begins to fall on her bare skin. The cold droplets become slick metal, webbing over her head, her shoulders. She closes her eyes and lets herself be lifted up into the dark.