The alarm shrieked again, like needles pressing into our ears. When it stopped that time, my ears were ringing, and Malachi’s voice was murky when he spoke. Even so, I understood his words.

“Fire suppression,” he said. “It’s venting the oxygen.”

In the silence that followed came a soft, steady hiss. It was the same sound that had followed the same wailing alarm on Dr. Summers’s last log entry. The same bright light.

They meant to suffocate us. Malachi was already moving. He spun around and kicked himself toward the door.

“There has to be a fail-safe,” he said. “It can’t—”

The alarm screamed.

“—in case somebody’s trapped,” he finished.

He tapped frantically at the panel by the door, but the door remained stubbornly locked. The alarm screamed again. It had been so long since I’d seen him in bright light; he looked tense and exhausted.

“Help me!” he shouted.

I searched the workstation, the instruments, the array of computers lining the walls. Help him, help him—but I had no idea what a fail-safe mechanism would look like. This was not a test of loyalty. This was not punishment. They would not return. How quickly they had made the decision. How quickly they had left.

“Zahra!” Malachi shouted, after the alarm sounded again. “Zahra, snap the fuck out of it and help me.”

I looked up quickly, turning my head so fast it sent a wave of dizziness over me. I had never heard Malachi sound like that before, so angry and sharp. There was no waver in his voice, none of his usual quavering uncertainty. I blinked once and nodded. The cold, the thinning air, they were taking their toll, but I had to concentrate. I pushed away from the support strut and caught myself on the workstation screen—the metal was so painfully cold it burned my skin—and twisted myself up, grabbing for the open panel on the probe. I kicked up from the stool for momentum and launched myself to the other side of the probe.

I caught Dr. Summers’s corpse about the middle. As we floated toward the far wall of the laboratory, I began searching through the pockets of her jumpsuit. In the first I found a gold ring, half of a protein bar, a couple of small screws. In the other, only a pocketknife, not quite ten centimeters long. I let out a growl of frustration. We needed a way out. We needed more time. The hissing had grown louder. I winced, trying to turn away from it, but there was no escape. There was a ventilation panel high on the wall, right over the head of the other corpse.

And on the panel’s edge a neat label: INTAKE/OUTGO.