She shook her head. "It doesn't tell me a story, yet." She picked up a piece and handed it to me. "Tell me what you think about this one."

It was a curved piece of aluminum, forty-centimeters long, somewhat bent.

"Exterior habitat pressure-vessel wall," I said.

"Right so far. What else?"

The piece had broken at a seam at one edge. Shoddy workmanship? Probably not; the other end had ripped jagged right across; the weld had probably never been designed for the stress it must have taken. It was bent in the middle. The jagged end had a sc.r.a.pe of paint on the raw metal. "Blue paint chips on the end here," I said.

"Right," she said. "And the bend?"

It took me a moment, but suddenly I saw it. "Bent the wrong way," I said. "It bowed in. The explosion should have blown it out." I thought for a moment.

"Could have been bent by the wind, later."

She nodded, thoughtful. "Possibility. There are other pieces bent the same way, though."

"How much overpressure would it take to bend it that way?"

"Good question," she said. "If we could figure the overpressure as a function of position, we can guess the locus of the blast. Turns out, though, that it doesn't take much blast pressure to make the habitat structure fail this way.

The pressure vessel was designed to hold an interior pressure; it's not well designed against an external overpressure."

"So, what do you think?"

"It might have failed in the rarefaction rebound following the overpressure of an explosion," she said. "Microstructural examination might tell. Might not."

"Or the explosion was outside the habitat." That would make sense. If somebody had wanted to kill the team, the easiest way to do it would have been to put a bomb next to the shelter.

Leah shook her head and chose another piece to hand to me another. "Carbon deposits," she said.

I looked at it and nodded. The burn marks were on the concave side, the interior. "Fire after the blast?" I suggested.

She nodded, but slowly. "Could be, I suppose. But after the habitat breach, everything vents to the reducing atmosphere. Fire goes out pretty quick."

"If it was murder," Leah said, "Who might have done it?"

We were sitting back in the little conference room. My whole face itched now, despite the ointments that Tally had devised for sunburn. My face felt like I was still wearing the rebreather.

"Hard to say," Tally said. "I suppose either one of 'em might have had enemies.

If it wasn't personal, I've got a few possibilities. First, before they went, turns out they got a couple of anonymous messages saying not to go. The point was, Mars was property of Freehold Toynbee, and it was reserved for the Martians, however long it took them to appear. Humans were expressly forbidden to land."

"Toynbee!" Leah said. "They were dissolved more than a century ago. Bankrupt and sold for sc.r.a.p. Besides, lots of researchers have visited Mars."

Tally nodded, slowly. "A century ago, yes. I doubt anybody been here in the last hundred years, though, except our poor friends. Seems hard to believe anyone would still care. A nut, I'd say. Still, a nut might be what we're looking for."

"And the other possibilities?"

"Turns out that there are still some people," Tally said, "as think that ecopoiesis is usurping the role of G.o.d. And some as think that ecopoiesis is, or was, a crime against the ecosystem. And there's been talk that if Mars could be triggered, then other planets, in other solar systems, could be. Some of these have life of their own, incompatible with terrestrial life. So, some radicals, they don't want Mars studied. They're scared that any studying of Mars is a step to triggering planets in other solar systems. There are those as would like to stop that. Stop it early, and stop it at any cost.

"And, finally, there are those as worry about Mars, worry that this ecopoiesis might just be another LA waiting to happen." She shrugged. "Me, I rather like old LA. Got that kind of raw charm you don't see much in other cities nowadays.

But I know that not everybody thinks like me."

"I see," said Leah. "And which of these would have set a bomb?"

Tally shrugged. "Any of them. Or all of them, working together."

"Working together? Logically, the Toynbees and the eco-radicals are enemies."

Tally smiled. "Logically, we're not precisely talking rational people here."

"So what do we have?"

"See, are we even sure it was a bomb?" Tally said. "Tinkerman, you find any suspicious pieces of pyrotechnic?"

I shook my head. "Nothing yet. But I don't know much about bombs. I might have missed something."

"Me neither," Tally said. "And I do know about bombs, I do. A bit."

Leah Hamakawa was completely opaque to me. I never had a clue what she was thinking, what she felt or thought about me. Sometimes her gaze would wander over me and stop, and she would look at me, not with a question, not with an invitation, just a look, calm and direct. I wished I knew what she was contemplating.

I wished I knew why I was so attracted to her.

The trip to Old LA had been a cusp in our relationship. On the trip we had just been fellows, co-adventurers and nothing more. Afterwards, Leah accepted the fact that I tagged along after her as just a facet of the environment, hardly worth commenting on. We're not, actually, a team, although it must seem like it to others. Leah was the hotshot scientist, and, well, every team needs a tech and a pilot.

Eventually she had noticed.

"Look," Leah had said. "You're as skittery as a colt, you're stammering, I can't get one full grammatical sentence out of you in a cartload, and you're so nervous I'm sure you're going to break something. Do you want to sleep with me?

Is that it?"

Her gaze was direct. It was always direct.

I couldn't say anything. I had trouble closing my mouth, "If you do," she said, "fine, do it, or don't do it, I don't care, just will you quit stumbling around."

And, later, after she'd taken off her clothes, she said, "Just don't think it means something, okay? I couldn't stand that."

But it did. Maybe not to her, but to me.

And so we came to Mars. When the authorities had finally noticed that the missing science team had stopped filing status reports to s.p.a.cewatch, and the orbital eye they sent to report got a break in the heavy Martian cloud cover and saw pieces of the habitat spread across ten kilometers of landscape-- a "presumed fatal malfunction," as it was reported, s.p.a.cewatch had asked for Leah; she had a rep for unraveling tough b.a.l.l.s of fur, and I scrambled to rate the slot to go along. Not that this was so hard; I had my skills, piloting and mechanicing and, yes, troubleshooting, and most crews were glad to have me aboard. In this investigation, the third slot on the team was special, in case the accident we were investigating was no accident at all, and the perpetrators might not be finished. The third slot needed a professional paranoid.

We both knew exactly the survival expert who was right for that place "Still hanging 'round with that long-legged white girl, I see," Tally had greeted me, when I came to ask if she wanted to join the team. "Give it up, boy, she's too good for you."

"Don't I know it," I'd said.

But that was the past, and brooding over the past wasn't going to get me to bed, or explain Leah Hamakawa to me. She had undressed without the least trace of self consciousness and gotten into the cubby's tiny bed. I undressed, with a lot more trepidation, and lay down beside her. She turned and watched me with a pellucid gaze, free of any emotion I could interpret. She wouldn't let me understand her, but for whatever reason of her own, she would let me love her.

For the moment, that would have to be enough.

The next day I worked on decoding the data from the damaged opticals, while Leah put together the jigsaw puzzle of the exploded habitat pieces, and Tally ranged in ever wider loops from the habitat, exploring. I succeeded in getting large blocks of data, but nothing was of any evident value: lengthy descriptions of bacteria, lists of bacteria count per square millimeter in a hundred different habitats.

"Here's something," Leah said. "Take a look at my collection of pieces. What's missing?"

I looked over the junk pile. Skin, electronics, window fragments, plastic shards. "What?"

"Don't you see it? Aluminum, t.i.tanium, carbon-composite, plastic-- anything missing here?"

Now that she had given the hint, I could see it, too. "Steel. Nothing out of steel, or iron. Is that surprising? Steel's heavy." Hardly anything in a s.p.a.ce-going technology is made out of steel. In s.p.a.ce, every extra gram is paid for over and over again in fuel.

"There's not a lot of steel on a hab module," Leah said, "but there is some.

Look around our hab, not everything is made of the light metals. But, no steel in the pieces here. And, take a look here." She chose a piece out of the pile and handed it to me. It was a damaged recording unit. The capstan flopped loose in the absence of the steel axle it should have rotated on. She handed me another, a piece with a neat hole where a steel grommet should have fit.

"Does that mean anything?"

She shrugged. "Who can tell? Probably not."

"Any steel fixtures hold pressure?"

Leah shook her head. "I checked the plans. No, all the iron and steel parts are incidentals. No steel penetration of the pressure hull."

Tally came back from her scouting, and looked at us both. "You are working too hard," she said. "It's time for a break. Way past time, you ask me. And I know just the thing."

"What do you have in mind?" I asked.

"Here." She handed me a sheet of aluminum. It was about a meter long, slightly curved, one side coated with a carbon composite facing. In a corner "117 Outer"

was written in Leah's neat printing. A panel from the outer skin of the exploded habitat. A mounting f.l.a.n.g.e with a hole for bolting interior fixtures was at one end. She handed another one to Leah. "Sure you don't need these panels, now?"

she asked Leah.

"Already looked at them." Leah shook her head. "That was the side opposite the explosion. Nothing but junk, now."

After we had suited up for outside and smeared one another's faces white with sunblock, we each took a panel, and Tally led us up to the top of the ridge that rose above the habitat. The hill surface was comprised of sand held in place with a thin veneer of purple-brown algae, slick as powdered Teflon. We had to choose our footing carefully to avoid skidding back down.

It was a gorgeous day. From the ridge, the marscape appeared striped, brown and purple strips in alternation all the way to the horizon. The purple was the algae, covering the sunnier face of each ridge; the brown anaerobic sc.u.m colonizing the shadier back face. The characteristic north-south wind pattern was clearly manifest in the form of long streaks trailing behind each of the larger boulders. Today, though, the wind was once again slight, erratic light gusts of no fixed direction.

We reached the top, and Tally smiled. She threaded a lanyard through the bolthole on her aluminum sheet, dropped it on the ground, and put one foot on it. "You might try this sitting down first," she said. Holding the lanyard in one hand like a set of reins, she pushed off down the hill.

At first she didn't move very fast. As the sled gathered speed, each b.u.mp sent it increasingly higher. Her balance seemed precarious, but in the one-third normal gravity of Mars, she had plenty of time. As she leaned to control the sled, her movements were a slow-motion ballet. We could hear her shout, m.u.f.fled by her rebreather, trailing behind her.

"Yahoo!"

I looked at Leah. She looked back at me, then shrugged. She dropped her sled on the ground and pushed it with her toe, testing how well it slid over the sc.u.m.

Then she sat down on it, grasped the lanyard with both hands and pulled it taut, and looked back over her shoulder. "Give me a push," she said.

It took a little more skill than Tally had let on, but after a few spills, we got the hang of it, and organized sc.u.msledding races. Tally on one sled and Leah and me together on another, then Leah and Tally together, then finally all three of us on one sled, Leah and I sitting docked together and Tally standing with her knees gripping my chest from behind.

At a rest break, sitting exhausted from climbing, I said to Tally, "So this means that you think there's no danger? I mean, n.o.body trying to kill us?"

"Never said that." Tally shook her head. "No, I'm not about to be calling all-clear, not quite yet. But I'm pretty sure that there's no danger right exactly this instant. Not unless these killers are invisible and don't leave footprints." She paused. "And, 'sides," she continued, "this is pretty much the tallest ridge in the area. If they were coming for us, we'd see 'em miles away."

"But what if we did? What could we do? We'd be sitting ducks."

Tally grinned a broad grin. "Sitting ducks, you say? Take a peep that ridge over there." She pointed.

I looked. Nothing special, no different than any other ridge. "So?"

I had glanced away for only an instant, but suddenly Tally had an omniblaster in her right hand, a knife in her left, and a projectile rifle with an infrared targeting scope resting at her feet. I had no idea how she could have concealed such armament on her.

"How bout you?" she said. "Don't tell me you're naked?"

I was far from naked--the temperature couldn't have been more than a few degrees above freezing-- but I wasn't carrying a weapon.

"Didn't I tell you to always wear a gun?" she said. "Dangerous out here. Who knows who might want to shoot you?"

"Carry an omniblaster? No, I don't think you ever told us that."

"Yes I did. Told you both. Back in OLA." She paused for a second. "s.h.i.t. I bet Leah's walking around naked, too." She shook her head. "You two just a bunch of children. I'm surprised you've lived this long, I really am."

"Say, look," said Leah, coming up behind us. "The sun's out."

We both looked up. The sky had been steadily overcast ever since we had landed, but the clouds were breaking up, and between them we had a glimpse of the sun.

"Take a look at that sky!" Tally said. "Isn't that gaudy!" Behind the clouds, the Martian sky was a startling blue, a bright, nearly turquoise shade that I'd never seen on Earth. I couldn't think of a reason offhand why the sky should be a different color, but, naturally, Leah could.

"Methane," she said, after a second of thought. "After carbon dioxide, methane is the main atmospheric component here. Strongly absorbs red light, so the sky color is a deeper blue than just the Rayleigh scattering would predict."

"Oh," I said.

"Explains why the colors here are so muted," Leah said.

With the sunlight, the wind had picked up as well, a steadily rising wind out of the north. Suddenly the coveralls we had on weren't enough to keep us warm. We ran for the habitat.