Doris said something obscene. Prax looked up at her. She ran a hand through her thin white hair, turned, and spat.

“Lost connectivity,” she said, holding up the hand terminal. “Whole network’s locked down.”

“By who?”

“Station security. United Nations. Mars. How would I know?”

“But if they—”

The concussion was like a giant fist coming down on the cart’s roof. The emergency brakes kicked in with a bone-shaking clang. The lights went out, darkness swallowing them for two hummingbird-fast heartbeats. Four battery-powered emergency LEDs popped on, then off again as the cart’s power came back. The critical failure diagnostics started to run: motors humming, lifts clicking, the tracking interface spooling through checksums like an athlete stretching before a run. Prax stood up and walked to the control panel. The shaft sensors reported minimal atmospheric pressure and falling. He felt a shudder as containment doors closed somewhere above them and the exterior pressure started to rise. The air in the shaft had been blown out into space before the emergency systems could lock down. His dome was compromised.

His dome was gone.

He put his hand to his mouth, not realizing he was smearing soil across his chin until he’d already done it. Part of his mind was skittering over the things that needed to be done to save the project—contact his project manager at RMD-Southern, refile the supplemental grant applications, get the data backups to rebuild the viral insertion samples—while another part had gone still and eerily calm. The sense of being two men—one bent on desperate measures, the other already in the numb of mourning—felt like the last weeks of his marriage.

Doris turned to him, a weary amusement plucking at her wide lips. She put out her hand.

“It was a pleasure working with you, Dr. Meng.”

The cart shuddered as the emergency brakes retracted. Another impact came from much farther off. A mirror or a ship falling. Soldiers shelling each other on the surface. Maybe even fighting deeper in the station. There was no way to know. He shook her hand.

“Dr. Bourne,” he said. “It has been an honor.”

They took a long, silent moment at the graveside of their previous lives. Doris sighed.

“All right,” she said. “Let’s get the hell out of here.”

Mei’s day care was deep in the body of the moon, but the tube station was only a few hundred yards from the cart’s loading dock, and the express trip down to her was no more than ten minutes. Or would have been if they were running. In three decades of living on Ganymede, Prax had never even noticed that the tube stations had security doors.

The four soldiers standing in front of the closed station wore thick plated armor painted in shifting camouflage lines the same shades of beige and steel as the corridor. They carried intimidatingly large assault rifles and scowled at the crowd of a dozen or more pressing in around them.

“I am on the transportation board,” a tall, thin, dark-skinned woman was saying, punctuating each word by tapping her finger on one soldier’s chest plate. “If you don’t let us past, then you’re in trouble. Serious trouble.”

“How long is it going to be down?” a man asked. “I need to get home. How long is it going to be down?”

“Ladies and gentlemen,” the soldier on the left shouted. She had a powerful voice. It cut through the rumble and murmur of the crowd like a teacher speaking to restless schoolchildren. “This settlement is in security lockdown. Until the military action is resolved, there is no movement between levels except by official personnel.”

“Whose side are you on?” someone shouted. “Are you Martians? Whose side are you on?”

“In the meantime,” the soldier went on, ignoring the question, “we are going to ask you all to be patient. As soon as it’s safe to travel, the tube system will be opened. Until that time, we’re going to ask you to remain calm for your own safety.”

Prax didn’t know he was going to speak until he heard his own voice. He sounded whiny.

“My daughter’s in the eighth level. Her school’s down there.”

“Every level is in lockdown, sir,” the soldier said. “She’ll be just fine. You just have to be patient.”

The dark-skinned woman from the transportation board crossed her arms. Prax saw two men abandon the press, walking back down the narrow, dirty hall, talking to each other. In the old tunnels this far up, the air smelled of recyclers—plastic and heat and artificial scents. And now also of fear.

“Ladies and gentlemen,” the soldier shouted. “For your own safety, you need to remain calm and stay where you are until the military situation has been resolved.”

“What exactly is the military situation?” a woman at Prax’s elbow said, her voice making the words a demand.

“It’s rapidly evolving,” the soldier said. Prax thought there was a dangerous buzz in her voice. She was as scared as anyone. Only she had a gun. So this wasn’t going to work. He had to find something else. His one remaining Glycine kenon still in his hand, Prax walked away from the tube station.

He’d been eight years old when his father had transferred from the high-population centers of Europa to help build a research lab on Ganymede. The construction had taken ten years, during which Prax had gone through a rocky adolescence. When his parents had packed up to move the family to a new contract on an asteroid in eccentric orbit near Neptune, Prax had stayed behind. He’d gotten a botany internship thinking that he could use it to grow illicit, untaxed marijuana only to discover that every third botany intern had come in with the same plan. The four years he’d spent trying to find a forgotten closet or an abandoned tunnel that wasn’t already occupied by an illegal hydroponics experiment left him with a good sense of the tunnel architecture.

He walked through the old, narrow hallways of the first-generation construction. Men and women sat along the walls or in the bars and restaurants, their faces blank or angry or frightened. The display screens were set on old entertainment loops of music or theater or abstract art instead of the usual newsfeeds. No hand terminals chimed with incoming messages.

By the central-air ducts, he found what he’d been looking for. The maintenance transport always had a few old electric scooters lying around. No one used them anymore. Because Prax was a senior researcher, his hand terminal would let him through the rusting chain-link fencing. He found one scooter with a sidecar and half a charge still in the batteries. It had been seven years since he’d been on a scooter. He put the Glycine kenon in the sidecar, ran through the diagnostic sequence, and wheeled himself out to the hall.