After sweeping Sean’s body and the rest of the level with his Eenspektor, Jiro floated down the gangway to the next level “down.” The noise of the Eenspektor built steadily.

“Oh, turn the fucking sound off,” Markus said, and it went quiet. It would now display the counts per minute on its little screen, which only Jiro could see, but they wouldn’t hear the clicks.

The next story was a sort of general meeting, dining, and muster room, mostly open space lined with storage lockers. The third, or middle, story was divided into sleeping compartments, toilets, and showers. The fourth was a laboratory and workshop space. Those functions continued down into the fifth and bottom-most story.

“Cold here,” Jiro said, as he reached the bottom level. “Suddenly a lot of beta.”

“Okay,” Markus muttered, “so the contamination is there. On the fifth level down.”

It was cold, as they soon saw, because someone had left the door open: a manhole in the middle of the floor, big enough for a person in a space suit to climb through it and into a round shaft leading straight down into the ice. The entire length of the shaft was illuminated by white LEDs.

“That is remarkable,” Markus said.

Jiro descended into the tunnel headfirst and began to propel himself along it by the simple expedient of pulling on a knotted rope that had been fixed into its wall by ice anchors. He moved tentatively at first, then more rapidly. “There is a hatch at the far end—a hundred meters away, maybe,” Jiro said.

“Radiation?” Markus asked.

“Not so much,” Jiro said. “I do not think this was the route of the contamination.”

The hatch at the end was adorned with a more formal rendering of the radiation hazard symbol. They all knew what was on the other side of it: a small pressurized module that was physically connected to the guts of the reactor. Jiro elected not to go through, instead turning around for a return to the command module.

Then he turned back suddenly, and swept the beam of his headlamp across the ice wall of the tunnel. Some long slender object was embedded in the ice.

Two long slender objects.

Two human bodies. Dinah gasped as she recognized Larz’s strawberry-blond hair.

Without making any comment, Jiro made his way back “up” the tunnel to the lower level of the command module. He turned his attention to a locker near the hatch. Its door was open. Mining tools and space suit parts were floating around in it. Others had spilled out into the room and were drifting around aimlessly, pushed by currents of air.

“Jiro,” Markus said, “talk.”

“Strong beta from here,” Jiro said. “This is where the contamination came from.”

He drifted back up to the common room and found a garbage bag in a cabinet, then returned to the bottom level and went to work sorting through the tools and the clothing, holding each of them in turn up to the Eenspektor as he focused on its screen. From time to time he would grimace at the results and push the item into the garbage bag.

Dinah, Markus, and Vyacheslav waited in New Caird for an hour, pretending to pass the time with tasks on the screens of their tablets.

Then they heard Jiro’s voice again: “Prepare to put something out the airlock!” he was shouting.

It took them all a few moments to understand Jiro’s thinking. New Caird and the command module of Ymir now formed a closed system. Since the latter was completely embedded in ice, the only way to remove something from that system—to take out the radioactive garbage—was to put it out New Caird’s airlock.

There were some distant thuds. Dinah floated forward and opened the hatch to be greeted by a garbage bag, filled to the dimensions of a beach ball, and all wrapped up in duct tape. Propelled by a shove from Jiro, this entered New Caird. Dinah pushed it up to Markus, who intercepted it and tapped it sideways into the airlock. Vyacheslav slammed the hatch behind it. Then they heard a hiss, indicating that the lock had cycled. The bundle was now adrift in space.

Jiro’s head, then the rest of him came through the port. He had stripped off the bunny suit and the respirator and presumably stuffed them into the garbage bag. He was sweaty and exhausted.

“Just like old times, my friend?” Markus said, referring to Jiro’s earlier career running cleanup at Fukushima.

“I don’t miss it,” Jiro said.

It was warm in the command module now, so they didn’t need the parkas. But they all used bunny suits when they went into Ymir, and stripped them off before going back into New Caird. Contamination was “sneaky,” as Jiro put it. The beta emitted by a microscopic speck of fallout could be hidden from the Eenspektor’s view by just about any random obstacle—and the command module was cluttered with those. So Jiro’s initial sweep was no guarantee that tiny beta-emitting particles weren’t still hidden in there. If such particles found their way into a lung, or the digestive tract, fatal radiation damage was likely to result. He had, though, identified a space suit glove on the lower level as being heavily contaminated, and found lower levels of contamination on some other odds and ends that had gone into that garbage bag and out the airlock. With luck all serious sources of contamination had now been removed.

BEFORE IT HAD TIME TO THAW, VYACHESLAV TOOK SEAN’S BODY down from the ceiling. Slava wasn’t a life scientist, but he was a jack-of-all-trades. Bundled up in parka and moon suit, he cut the sleep sack open as Jiro stood over him with the Eenspektor. He performed a cursory exam, then wrapped the body back into the sleep sack. He maneuvered it to the lower level, threaded it through the manhole in the middle of the floor, and then pushed it down the tunnel to the end, where Larz and the other crew member had been buried. There, he stashed Sean’s body against the ice wall.

Somewhat ruining their appetite, he reported on the findings of this impromptu autopsy as they got ready to eat a meal in the common room.

“Sean bled to death out of his asshole,” he reported. “He had an internal rupture of the bowel.”

“I picked up some beta through his belly,” Jiro added. “He was very emaciated at the end.”

“Meaning?” Markus asked.

“He swallowed a particle of fuel. Probably a fuel flea that got loose and somehow was tracked in here.”

“Fuel flea?” Jiro had used the term before. No one else knew what it meant. It had gone in one ear and out the other, just another bit of the tech jargon that was so ubiquitous on Izzy. Now that fuel fleas were killing people, it was time to learn about them.

“A tiny piece of uranium or plutonium that has gotten loose from a ruptured rod. As it throws off alpha particles, it zigs and zags around the room—conservation of momentum. So it hops around like a flea. The point is, it is small and it makes a lot of alpha. It lodged in a diverticulum in his bowel. It burned through his bowel wall and started a bleed that could not stop.”

Everyone pushed back their food.

“Okay,” Markus said. “We eat in New Caird.”

Once they had finished their meal, Markus told everyone that they needed to sleep, since they had a busy few days ahead of them. Jiro volunteered to take the first watch, and so the rest of them slept while Jiro stayed up going through logs and notebooks, assembling a picture of all that had happened on Ymir’s journey.

Suddenly they had a lot of space to spread out in. Dinah was tempted to retreat to the far end of the New Caird and get some privacy, but Markus insisted that everyone sleep down in the command module. New Caird might be free of radioactive contamination, but it was exposed to the direct hazards of space. A bolide strike would kill anyone in it. Whereas a beta-emitting particle, inhaled into the lung, would take days or weeks to incapacitate the victim—time during which they could do useful work.