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  "That isn't very promising," she remarked, as it clearly took them away from the base.

  "Don't start complaining yet," A.J. said. "I'm still picking up water concentration."

  "Full stop!" Madeline said from just ahead. Cautiously, they moved up at her signal to take a look.

  The tunnel seemed to end here, until they got close and saw that what happened was that the tunnel itself had been essentially beheaded. A short bit of it remained ahead of them, while at their feet a wide crack dropped vertically into the depths. It was two meters across and much longer than that. From their current vantage point, they couldn't tell how much longer.

  Madeline shone her light down the crack. There seemed to be a floor, over a hundred meters down. "Good enough, I think. Helen?"

  The paleontologist agreed. "Yes, we'll make the descent. One at a time. I think you should go first, A. J., then me. Madeline, you bring up the rear since I think you're our best climber in case something goes wrong." She cocked her head. "Am I right?"

  "Probably. I spent some time on the Matterhorn, once."

  Seeing Helen's eyes roll in her helmet, Madeline protested: "Hey, it was just for the fun of it! I was on vacation, and I rather enjoy danger sports."

  Now A.J. was rolling his eyes.

  "It's true!" Madeline insisted. "The only top secret involved is how I managed to evade the attentions of Swiss males with too much testosterone and too little common sense. That's still classified. My boss is real big on contingency planning. If Switzerland ever drops her neutrality and becomes a U.S. ally, he thinks I might have to go in and establish the security for their chocolate recipes."

  Chuckling, A.J. dropped another bread crumb and began to lay out the climbing gear, while Madeline and Helen judged where best to put the pitons.

  The descent was made quickly. Getting back up would be a bit more tedious, but they had a powered ascender device that would be able to bring at least one person up to the top. From there, with muscles on top and bottom working against low gravity, they should have no problem getting the other two out.

  The crack became much broader as they went down. Once they were at the bottom, they could see that it had gone from two meters across to at least thirty meters. The length was still impossible to determine.

  There were no fewer than three tunnels exiting nearby. A.J. set his sensors in each one and after several minutes declared that he couldn't tell which way to go. The water vapor concentration in each was roughly equal, at least to the limit of what he could analyze at this point.

  "Which way is the base?" Helen asked.

  Seeing A.J. point, she nodded at the exit closest to that direction.

  "Then let's try this one."

  "Works for me."

  Narrower than the others, this passage required them to go single file and watch their heads. It twisted and turned and A.J. used three more bread-crumb relays.

  "How many of those do you have left?"

  "Forty-five. Believe me, I came prepared, especially after my experiences with that 'block out everything but gravity' stuff on Phobos."

  "It appears to be widening," Madeline said. Once again, she was in the lead. "I think I see a larger area in front of us."

  They emerged into a cavern and shone their lights around. "Oh, my God," Helen breathed.

  They were now probably three hundred meters down, below the floor of Thoat Canyon by a considerable distance. The cavern loomed above them, its ceiling nearly fifty meters above their heads and its sides disappearing into the darkness beyond the reach of their lights.

  But it wasn't the impressive sides that caught their attention. It was the diamond-bright sparkle from above, where pure white shimmering crystals hung from every point, where long stalactites glittered like diamonds, where other surfaces were coated with a luxurious white fur.

  "Ice," A.J. pronounced.

  Helen found herself almost unable to speak for a moment. Partly because the faint worry that they might run out of water if the reactors malfunctioned had now vanished. But, mostly, just because the fairylandlike sparkle was visually stunning.

  After a while, though, she began thinking of the puzzle involved, and its possible implications. "How could there be that much water here? In this atmosphere? Could any fossil deposit have lasted this long with direct openings to the outside?"

  "Might not have to," Chad Baird's voice broke in. Apparently the scientist had been listening to their transmissions. "One of the major theories—still being debated, but it's got strong support—is that Mars actually has a water table. Clearly it used to have a huge amount of water, and the theory is that a lot of it remains underground, maybe a kilometer or two. If so, what you may have is one, two, or three different interacting layers of water transport depending on depth, temperature, pressure, and some other less important factors. In that case, what might be happening here is that the fossil ice sublimes, gets redeposited in the caverns you've reached, and is at least partially replenished by water vapor percolating up through the soil beneath. Remember, you're way down below the general level of the ground there in the Valles. So if there is a water table, you're a lot closer to it. And with what you're seeing, that sounds more likely than ever."

  Helen nodded, still staring. "And if sublimation and redeposition is keeping these structures around in this volume, there must be a fair amount of water farther down here."

  A.J.'s enthusiasm came to the fore. "Let's find that base!"

  Across the cavern they walked, cautiously. After they found many signs of impacts, they kept a wary eye on the inverted faerie realm above, in case one of the ageless decorations decided to become a slow-motion plummeting missile.

  It was Madeline who spotted the path that led upward in the direction of the base. It looked strange, as if it were made of melted wax or something similar. None of them could decide if it had been created by nature or intelligence.

  Surprisingly, A.J. held out for natural causes. "We know there were aliens about so we tend to think everything weird is their doing. But I'm betting that Mars itself has got more weird saved up for us than Bemmie could have cooked up in the short time he was here. Maybe it's something left over from the era when Mars had lots of running water."

  "Doubtful," Baird commented. "A lot of the rocks involved in water deposition are, themselves, fairly heavy with water content. They tend to disintegrate in this kind of atmosphere as they dehydrate. But you have basalt over the top of the area, so it's possible that you're looking at something caused by volcanic action eons ago."

  The steep path, if that's what it was and not some kind of lava-flow or other natural channel, took considerable time and effort to climb. Finally, they stood at the top and looked down a tunnel about the same size as the last one. Helen eyed the ceiling suspiciously; there were signs of cracking at intervals along the way.

  And then they rounded the corner and found the door.

  The construction of the doorway was similar to those found in Phobos base, but clearly not identical. A.J. sent back high-resolution pictures in all spectra to Thoat. Inside the rover, Joe studied the doorway and other structures partially visible around the door before they disappeared into the rock at either side. He looked at them both in normal imagery and the more esoteric, partial imagery A.J.'s sensors could extract out of the stubbornly shielded material.

  "It's not the same," he said finally, "but it looks like the same kind of technology was involved. That's the best way I can put it. It doesn't differ from the Phobos designs nearly as much as those do from ours. It's more like the difference between Egyptian and Greco-Roman architecture."

  "So you think it's the same species, in other words." There was a note of disappointment in Madeline's voice.

  "That'd be jumping to conclusions," Helen said. "I can think of other possibilities. To name one, this could have been built by a different species—including a hostile species—but one which had been in contact with the Bemmies long enough for their technological
methods to have gotten largely shared. The way that, nowadays, an office building in Tokyo or New Delhi doesn't look that much different from one in New York or Barcelona. For that matter, if aliens had examined the Japanese planes that fought at the battle of Midway, they'd have had a hard time seeing much difference from the American ones."

  "True," A.J. said, "provided the two species were physically similar enough. Even if we shared technology with Bemmie, there's still no way we'd design a lot of things the way they do. Or vice versa. That door's quite a bit taller than I'd expect a Bemmie door to be, for instance. Although it could've been a small cargo door, I suppose."

  "How about getting it open?" Madeline asked.

  "Brute-force it," Joe proposed. "You don't want to try anything involving arc-cutting in there."

  "Why . . . oh."

  "'Oh' is right, A.J. You want to find out what it's like to be on the inside of a giant neon light tube? At the least you'd probably fry your electronics, and at the worst you'd fry yourself. The pressure's slightly higher down there, but I don't know that it would make enough difference—and we sure don't want you to be the experimental guinea pigs. No way around it. You'll have to come back here and get some of the excavation equipment."

  A.J. sighed. "Oh, now that's going to be fun. Even with the low gravity."

  "Well, you could just come back and forget about it, and we all just sit around swapping jokes until the rescue shuttles get here in a couple months."

  "I do not think so," Helen said firmly. "Okay, guys, let's head back. Tomorrow is going to be a big day."

  Madeline's voice was resigned. "More like tomorrow and the day after, at least. I've done operations like this before—don't ask where or why—and I think you're underestimating the difficulty we're going to have getting that equipment down here."

  Helen thought the security specialist was probably right. But she didn't really care. She was bound and determined to get into the base. If that meant dragging equipment deep into Martian caverns, well, it couldn't be that much worse than setting up a major dig.

  She led the way, as they left, already working on the problem. "We'll need to set up a field camp and supply area for this operation. We don't want to have to travel all the way back to Thoat and main camp whenever we run short of a few items. The exotic location aside, this isn't fundamentally much different from any major dig. When you're out in the badlands, you don't hop in a vehicle and drive off every time someone's thirsty and wants a soda."

  "Yeah, sure. But at least you didn't have to worry about bringing your own air supply."

  "Shut up, A.J.," Madeline growled. "Besides, even that's really no big deal. I once spent four weeks in a camp so high up in the Himalayas we had to haul in oxygen. It was a pain, but not that bad."

  She didn't start laughing until A.J. was choking audibly. "Just kidding. I didn't really spend four weeks on the slopes of Mt. Everest."

  "Well, praise be for small favors," A.J. muttered.

  "It was only eleven days—and it was on the slopes of Denali in Alaska, not Everest in Nepal, and it wasn't so high up that we needed oxygen tanks very often. I won't tell you which slope, though. That's still classified because my boss thinks someday the Athabascan Indians might—"

  "I don't want to hear it, Madeline!"

  Chapter 48

  "Okay, people," Joe said, several days later. "I think your best bet is to use the 'ripper' on the door."

  He and Bruce were the only ones remaining topside. With the alien base discovered and the strong possibility of new writing being found inside, Rich was now on site with Madeline, A.J., and Helen. Joe hated being left behind, especially since as an engineer the alien base no doubt held as many exciting possibilities for him as it did for anyone else. But dragging a broken-legged man through tunnels didn't appeal either to the others or even to the broken-legged man himself.

  Helen felt sorry for him, but at least it kept him in the safer area. She didn't feel very confident about the safety of these underground mazes, no matter how placid Mars' geology was supposed to be.

  Neither, to her dismay, did Chad Baird. "Be very careful down there, Helen," he'd said. "Yes, Mars is geologically stable compared to Earth. But that's just an average, on a planetary scale. Any particular spot on Mars might be far more dangerous than most places on Earth. And while I'm fascinated by what you've found down there, I really don't like the looks of it, from an explorer's standpoint. Whatever the mechanism is that created those ice caverns, it has to be a fairly active one or the ice wouldn't still be there at all. And now you'll be introducing a new disturbance. So be careful."

  Unfortunately, A.J. had been there to hear the conversation. For two days thereafter, he'd gone around periodically intoning lines from an old science fiction movie: Be afraid. Be very afraid.

  Joe thought it was funny.

  Joe would.

  So, Helen had insisted on delaying the operation until they could put whatever supports and braces they could design and make in that last run of tunnel that had cracks in the roof.

  It wasn't much, since their material supplies were limited. Mars gave up no wood for timbering, of course. But at least they had a comparatively secure route from the door to their field camp and supply dump. They'd set that up at the base of "Melted Way," the odd path that led up from the large cavern.

  Madeline and A.J. dragged the "ripper" towards the alien door. Unlike the sort of rolling-valve doors found on Phobos, this door seemed to be designed to split in the center and slide up and to the side. This made the "ripper," a bastard descendant of a forklift and the jaws of life and a few other gadgets, ideal for the job. It could insert its pair of flattened-tine lever arms into the crack in the door and pull it apart by main force, assuming the door wasn't stronger than a bank vault.

  A.J. positioned the lever arms above and below the area where he believed there was a sort of bolt or other fastener according to his sensors. Then, he and Madeline braced the ripper—which he'd promptly nicknamed "Jack"—solidly against the rock walls with its built-in extensible supports.

  "Okay, everyone clear back. We don't want to take any chances on being hit by something if either the door or Jack breaks."

  No one debated that. All four of them returned to the top of Melted Way before A.J. sent the command.

  "Okay, Jack—let 'er rip!"

  They were able to watch the operation on a screen, from sensors left on site. The fuel-cell-powered ripper hummed, and there was a sudden screeching noise audible all the way down the corridor as the lever arms inserted themselves forcibly into the narrow crack between the door valves. The humming abruptly dropped in pitch and became louder as it began to force the doors open.

  A.J. watched telltales on the sensors rising. The stress built up, started to edge towards the caution zone. "Stop."

  "No go?" Madeline asked.

  "Bah. I have not yet begun to fight. I just don't necessarily see that I have to do it in one pull. Repetition and overstrain, that's the key. The same way you break a piece of metal by continually bending it back and forth. I'm betting that after umpteen million years, even that alien material is subject to being fatigued."

  At A.J.'s direction, the ripper began a series of sudden, very high power pulls, none of which lasted long enough to endanger the machine. The ripper also began moving the tines up and down and trying to twist them, exerting force along most of the length of the opening.

  Then A.J. ordered it to give another long pull.

  With a suddenness that caused them all to jump, the door split wide open. The ripper emitted another high-pitched whine before shutting down.

  "We're in!" A.J. announced exultantly.

  Once they arrived at the door, they moved the ripper out of the way and retracted its supports. Then, slowly, they entered the alien base.