She remembered the lectures and the diagrams about oxygen starvation. They seemed distant and unreal. Bursting capillaries, straining heart—just words.

She grimaced. There was nothing to do but sit here and pass the time, wait to die. That was why she was here anyway, because she waited for things to happen. If she had stood up and said she didn’t want this job, they wouldn’t have sent her out here. Her flight reflexes were excellent, yes, she was light, they checked all that and more. But she always felt uneasy about it, as though she was missing some talent the others had. Maybe simple mechanical abilities—she was an electronic technician, really, not a mechanic.

But she was qualified, she could spot the likely sites for water boring from above and pilot skillfully around them for a better look. She was young and had endurance and was reliable. So she started the flights and got used to them, coming and going on her own schedule with the warm, smug feeling of being free to travel on a world where others spent their days inside cramped laboratories, buried ten meters inside the moon’s gray skin.

Come half of a million kilometers, she had told her parents, to be locked inside? See so little of those cold hard mysteries around them, have no adventure? So she thought, feeling glamorous, and forgot the danger.

It was easy to relax into the routine, just as it was so deliciously simple to learn the sled’s acrobatics, memorize the quilted green map, make herself ready.

It was the same with Toshi back on Earth, before all this. She had sat there certain of her status, sure Alicia presented no threat, and the girl took Toshi away almost without a nod. She had let Alicia take him, found it easier to be silent and pleasant and smiling, the same way she was forced into this job, and now she was going to die for it, gasp out her last breath because she recoiled from the heat of conflict, couldn’t take that tight nervous clenching in the stomach—

Slowly, very slowly, she stood up. The idea was only a glimmering, but as she turned it over in her mind it became real.

But could she lift the sled? She’d never tried. Was there some way to do it? Alphonsus would know, they had more experience in these things, she could call and ask—ridiculous, no, there was no time for that. She turned and started walking smoothly, evenly, saving her energy. The dust crunched beneath her boots and she studied the sled intently as she approached.

Black shadows hid some detail, but she was sure the knock-off joints near the couch were not damaged. The sled was made for quick disassembly, segmented into modules that separated for maintenance.

Lift it? Impossible; it massed nearly a thousand kilograms. Nikka began to work. She disconnected pipe networks and wiring configurations and split off several of the supply flasks. She worked quickly, methodically, measuring each movement to conserve energy. Each valve seated firmly, each strut folded away. The knock-off joints snapped away cleanly and the sled broke in two. The tangled mass of the front was free.

The landing wheels were hopelessly crushed, but the front section was lighter than the other two-thirds of the sled; the ion engine was most of the sled’s mass.

Nikka walked around to the crumpled fender and found two good handholds. Even bent over in the light gravity, she could still get good footing by brushing away the blanket of powder beneath her boots. She set herself, got a good grip and pulled. The sled section seemed to resist, caught up on a small outcropping and then slid, slid over the dust. She grunted, pulled, it slid further. The dust was a good lubricant and once started, the sled section would glide for several meters with one pull.

Gradually, she worked it toward the hillside. It left a ragged track in the brownish dust and she lapsed into a rhythm—pull, take two steps, scrape dust aside so that she could get a good purchase on the rocks beneath, pull again. Her arms and legs strained and her back ached. Her air was beginning to foul, curling through her helmet with a weight of its own. It was a long, weary struggle to the invisible shield, but each step brought her closer and after a while her euphoria made the sled section seem lighter. She almost thought she could hear the brass as it scraped over rocks, mingling with the crunch of dust underfoot.

She should have called Alphonsus. They should know what she was doing. But they would find the dome whether they reached her in time or not. She was absolutely alone; life depended solely on her own effort.

Nikka was panting heavily by the time she reached the invisible demarcation. She bumped into it, nose pressing against faceplate. She remembered the bloody nose and noticed the caked dry blood inside her nostrils for the first time. It seemed as though that had happened a year ago.

She stopped and studied the air bottles, rejecting the ones with obvious splits or burst seams in them. There were two at one end which seemed intact, but she could not read their meters because of the twisted metal wrapped over them. Stopping only an instant to judge, she detached a strut and wedged it under the sled section. By leaning against it she forced the front part of the sled against the invisible shield.

She couldn’t be sure this would work. The aluminum pipe had melted, but the sled had steel and alloys in it that might not. She leaned against the strut, keeping the pressure against the part of the sled nearest the bottles. In higher gravity she would not have been able to lift the sled, even with the strut as a lever arm, but in low-g she could. Her shoulders ached.

Quick darts of flame shot down her back. She could see no change in the sled bumper, but then it slipped slightly to the left. She adjusted her footing, moved the strut to support the sled’s weight and then saw that a dark fluid was dripping slowly downward from where the sled had been. It must be a liquid metal, running down the face of the shield. Nikka tilted the strut forward, increasing the pressure.

After some moments the front face of the sled began to blur and run together. The twisted metal sagged at one point, then another. Slowly, agonizingly, a thin stream of liquid metal began to stream down the face of the invisible shield. A thin gray vapor puffed from it. It collected in spattered pools on the dust below. The sled tilted again—each time Nikka adjusted her balance, canted the strut to better advantage and kept up the pressure.

Through the film of perspiration on her faceplate she judged the shifting weight of the sled section and tried to compensate for it. Her air was getting thick and close. She had to struggle to focus her attention. Occasionally she glanced up at the crumpled copper dome above. An hour or two before, she had never seen it, never suspected she would find something so strange and alien in the midst of a selenographic survey. If she ever got out of this she was going to find out what that dome was and why there was a shield around it. Maybe its defense systems were acting sporadically without knowing what they were doing.

The sled tilted to the left again and she quickly brought the strut around to correct its balance. The liquid metal now ran in a steady stream; a vapor cloud formed above the sled. The twisted metal slowly gave, rippled and flowed away; in one quick rush the last obstacle to the oxygen bottles melted and was gone.

Nikka dropped the strut and frantically climbed over the sled. She twisted at the oxygen bottles but they refused to give. She leaned over, feeling the blood rush suddenly into her head, and struggled to focus her eyes. A pipe had lodged against them, pinning them in their mounts. She pushed futilely at the pipe and tried to dislodge it. It was stuck.

She scrambled back to the side of the sled and found the strut again. If she forced it against a rock—there, that was it—and tilted the sled, so; yes, it rose up again, presenting the pipe to the invisible shield. She wedged the strut into place and then worked her way around, near the shield so she could use her body weight against the sled and tilt it further over. She strained against it; the sled gave a bit and then the pipe came up against the shield. Her hands were wedged firmly against the pipe and she could see that her right upper wrist was being forced slowly against the shield. The weight of the sled shifted further and pinned her hand.