The vault was supposed to be the safe part of the mission.

This is our sixth routine descent to Earth after years of an artificial life built on Mars. First, humans built vaults and domes on the moon. Then we had to accelerate the Mars evacuation fifteen years ago as Earth started collapsing, showing us that humans no longer belong on it. A lot of people were left behind in the evacuation. I am pretty sure the damage caused to Earth was entirely our fault.

I look at my watch. The year is 2067 and it's 10:03 a.m. Earth time. Pacific Time. Back when that used to mean something, at least. I smell the faint bitterness of the coffee bulb Darren never set down. I miss the scent of the planet's real brew. I never got to taste it, but the memory from when I was fifteen and living at my grandparents' house on Earth still lingers sometimes.

My jumpsuit clung at the small of my back where sweat had already gathered against the padded liner.

I felt a violent vibration start under my boots. A few seconds later, the alarms went off.

"Did you feel that?" Darren said. He was at his terminal, holding his coffee bulb with both hands to stop it from spilling.

"Mae. Did you feel it."

"I felt it." Mae was already on her feet. "Yuri, run a structure scan."

"Running." Yuri had his eyes on the screen. He had three rings on his right hand, and he turned the middle one when he was anxious. He was turning it. "Section C is reporting a pressure drop."

"Section C is empty," I said.

"Section C is reporting a pressure drop," Yuri said again, in the calm voice he used when he was telling you he had heard you and you were also wrong.

I closed my notebook and tried to still my shaking hands. This had never happened before. Fighting back panic, I reached to clip the pen to the cover, but it dropped straight to the floor.

The lights flickered.

"Remember when being an astronaut meant something," Darren said.

"Stop." Mae was at the comms board now. "Mars, this is Vault One. We are reading anomalous pressure failure in Section C and a low-frequency vibration through the foundation. Confirming you have telemetry."

The reply was a hiss.

"Mars, this is Vault One. Confirm telemetry."

Hiss.

"Mars."

Yuri said, "Mars is dark."

"Mars is dark," Mae repeated, the way you repeat something so your brain accepts it. "We've lost connection."

The vibration was through my ribcage now. I could feel it in the soles of my feet, and the lights flickered again, and Darren said, "People are so convinced Mars is an eternal beach life."

"Darren," I said.

"What."

"Stop complaining about Mars, this is serious."

He looked at me. He had a smear of toothpaste on his collar and I had not told him about it that morning. I had been saving it for later, the way you save small kindnesses for after you finish your shift.

"Yeah," he said. "Okay."

The bulkhead seal in Section C blew. I heard it as a single dry concussion, and the floor moved sideways under all four of us. The impact traveled up through my knees, a hard jolt that locked my teeth together and sent a sharp pulse straight between my legs. Mae caught herself on the comms board. Yuri didn't catch himself at all. I went down on one knee and stayed there, breathing in and out four times the way the Mars Colonial Institute had taught us to do during decompression drills. I had always thought those drills were stupid. They felt especially useless while locked inside a vault on a post-apocalyptic Earth. The floor felt colder through the fabric at my knee, the suit pulling tight across my legs with the movement.

"Move," Mae said. "Suit up. Move. Move move move."

I stood up fast and moved.

The corridor lights flashed red. I had never seen emergency mode outside of a drill, and the hallway I had walked through fifteen minutes earlier with a cup of synthetic tea was unrecognizable. Under the crimson glow, it looked like the inside of a living heart as loose gear flew through the air. By the time we reached the second door, my helmet was secure, but the gate was already locked.

"Override," Mae said into her wrist. "Override Tamura six six four."

It would not override.

"Override Park three nine one."

It would not override.

"It's not locked from comms," Yuri said. "Mae, it's locked from the floor."

"What floor."

"The floor." He looked at me, and he tilted his head, and I understood what he was saying. The floor was the structure itself. The vault was sealing us in section by section. Manually, maybe. Or by something that could lock from underneath the system.

"Section B is going next," Yuri said.

"How do you know."

"Pressure drop. I have the screen." He stopped. He started again. "Section B in twenty seconds."

"Section B is us," I said.

"Yes." His face went pale.

Mae was already running back the other way. Small as she was, she moved with an intense anger. That was how she approached every drill, which always made us laugh because Mae was the calmest person any of us had ever met. She was the calmest because she ran toward danger instead of away from it.

She got eight meters before the next bulkhead dropped. I did not see it clearly, it was just a vertical line of dark steel slamming down faster than gravity should allow. Mae slid forward at the last second, the steel hit, and the bulkhead settled into place. There was nothing left of Mae to see, yet it is all I will ever see for the rest of my life.

And then I saw nothing. The sound carried a wet compression that struck me in the chest, a deep throb that echoed low in my gut.

Yuri said, "Rei."

He was on the floor. He had not gotten up. His left arm was bent at an angle an arm should never form. He reached up to me with his right hand, the ring on his middle finger crooked where he had been turning it.

I knelt. The red emergency light made his face look already gone. I took his hand, the metal pressing against my palm. He had told me, on this trip, that his husband Aaron had given him the middle one. The other two belonged to his grandfather. His fingers were warm and damp where they curled around mine, the skin soft and alive against my glove.

"Rei," he said. "Go."

"I will."

"Go now."

"Yuri."

"Aaron knows," he said. "He always knew. Tell him…"

The third bulkhead came down between us. It was so fast I did not hear it. The bulkhead came down between his wrist and his elbow, and his hand stayed in mine, and I was still kneeling, and the corridor was a very small thing now, and the red light was very loud. The rings were still warm from his body heat, the severed warmth seeping into my skin.

I stood up.

I put Yuri's hand on the floor because there was nowhere else to put it.

The fourth bulkhead, the last one between me and the surface, was thirty meters down the corridor. Section A. The decontamination chamber. The airlock.

The lights cut out.

The lights came back on as a colder red.

Darren had been somewhere behind me. He had been right behind me. He had been right behind me the whole time. I heard him say my name, heard the next bulkhead go down between us, and then I heard him stop saying my name.

I ran.

I ran in the way you run when there is no decision to make. I ran past the door that had Mae behind it, past the door that had Yuri behind it, past the door that had Darren behind it, past my own thinking, toward the only door I had any chance of opening. The airlock. Thirty meters of corridor that was getting shorter by the second. My boots struck the grating in hard, even beats. The suit fabric rasped at my inner thighs with every stride, the seam catching and dragging over the swollen heat between my legs. Each step caused a sharp friction that made my breath catch.

I made it.

The airlock cycled anyway. It was old enough to run on a separate failsafe loop, designed to let you out even when the rest of the ship was trying to kill you. The outer door slid open. The wind hit my face like a solid hand. The sky was the color of rust and old paper, and the ground was just dust and strange shapes that looked nothing like any earth I had ever known.

I stepped out.

The vault sealed behind me with a sound that was almost a sigh.

I was back on a planet that hadn't been my home for three decades. No team, no plan. Then the memory of my grandmother caught me completely off guard. She spent her entire life on Earth, choosing to stay even when she earned a spot on the Mars evacuation. She never gave up on her home. Not like me, even if I had no choice.

"Welcome back to Earth, I guess," I muttered to myself, knowing there was no one left to hear it.

Somewhere out there in the vastness, something was watching me. I didn't know it yet. I only knew I was alone in the wasteland, comforting myself with the thought that the vault, at least, had been safe.

It hadn't.