The boat entered atmosphere over the daylight hemisphere and was quickly enveloped by the turbulence of the upper stratosphere. Despite Forbes's assurance that this was normal, Kimber began to worry. The shaking got progressively worse as they descended. Only the thick padding of her helmet kept her from injuring herself as her head bounced around freely inside. The turbulence reached a maximum as the boat crossed the boundary of the uppermost layer of clouds. Yet, when they finally broke out into thin haze, Kimber instantly forgot the discomfort she had endured. Her feeling for the planet overwhelmed her fear.

The boat crossed an ancient shoreline and dropped down toward the jagged inland mountain range where the energy screen laboratory was located. As they approached the landing site, Kimber saw a scattering of equipment around a tunnel cut into the side of a low hill. Mixed among the machines were three tiny figures in environment suits. She imagined one of them was Lars. At the thought of him, her heart began to beat faster.

Forbes made one circuit of the hill to check which way the wind was blowing, and then slowed to a hover on the landing boat's underjets. There was a brief flurry of dust and then they were down. Kimber waited with ill-concealed impatience for the pilot to raise the canopy. As she unbuckled her safety straps, a shadow fell across her. She glanced up to see a figure in an environment suit towering above her.

"Hello, stranger," Lars's familiar voice said into her earphones. "Welcome to Earth!"

She nearly stumbled in her haste to rise. Lars steadied her and then the two of them clasped arms. It was an unsatisfactory embrace encased in a centimeter of protective armor. Still, she imagined she could feel his touch as they pressed faceplates together to stare for long seconds into each other's eyes.

"How are things going?" she asked when he finally released her.

"Better than expected. We have excavated the laboratory entrance, sealed it as best we can, and have the refrigeration pack working overtime. The lab temperature is down to the high side of livable."

"Sounds lovely."

"Let's just say that it will give your sweat glands a good checkout. Where's your luggage?"Kimber gestured to the small bag that had been wedged behind her legs during the trip down from the ship. "That was all Captain McCarver would allow other than my suit."

Sands reached down in a movement that Kimber would not have thought possible. His time on the ground had obviously taught him a great deal about maneuvering in the bulky suit. He picked up the bag and steadied her as he led her across the wing toward the rear of the boat.

"Let me go first. I'll steady you as you come down the ladder."

"I can manage."

"Professor Eald said the same thing the day before yesterday. He very nearly broke his leg when he fell off. Be sensible. I don't want you getting hurt."

"As you will, my chivalrous knight!"

A minute later Kimber strode the dusty soil of Earth as she followed Sands toward the newly excavated tunnel entrance.

The long ramp had originally been cut from bedrock and lined with concrete, the terminus of a two-lane highway that had wound its way up through the foothills from the coastal plain below. Two centuries of flare weather had eliminated nearly every trace of the facility. The asphalt that had surfaced the road had softened in the heat and dribbled away in soft, black rivers of tar. The cut through which the road had run had slowly filled with blowing debris until it was at the same level as the surrounding ground. Beneath the surface, the concrete lining had cracked and fallen; leaving only an occasional patch of the manmade stone attached to the ramp sidewalls.

Kimber noticed these and a thousand other details as she followed Lars down the shallow incline that led into the underground installation. It was as though her senses had been sharpened a thousandfold as she swiveled her head from side to side to take in the sights. She could not remember ever feeling more alive.

"Watch your breathing," Lars warned.

"What?" she asked, drawing herself back from the wonders around her.

"You're starting to breathe erratically. It takes a conscious effort to control your breathing in these suits.

It's easy to hyperventilate."

"I guess I got excited," she said, puzzled at how he could know. Of course, she thought, he could hear her breath over the commlink just as she could hear him.

"Happens to everyone. You see something, get excited, forget to control your respiration, and end up dizzy. Don't worry. The excitement wears off after a few hours. Then you'll begin to notice the discomfort."

"That's something to look forward to, I guess," she said with just the right touch of mirth in her voice.

He led her down the tunnel and through an old airlock, but not one that had been part of the original laboratory. This construct bore the unmistakable signs of Saturnian manufacture.

"I don't remember sending this down from the ship," she said, fingering the fragile construct of lightweight beams and plastic sheeting."We didn't."

"Then thisis the place the Bormans investigated!"

"It is, indeed. We've found their garbage dump and a whole bunch of petrified food they left behind."

The airlock doors were simple sheets of thick plastic attached to the opening by strips of everstick tape.

Lars peeled back one strip and lifted the plastic sheet that served as a door. Kimber ducked inside and Lars followed. They repeated the ritual and were soon standing inside the gloomy laboratory interior.

"You can unsuit now," Lars said. He immediately reached up and began unsealing his helmet.

Out of habit, Kimber checked her helmet displays. Already the outside temperature readout was falling.

Conditions inside the laboratory were livable, but as Lars had intimated, far from comfortable. She reached up, unsealed her own helmet, and lifted it over her head.

She dropped the helmet to the end of its tether and inhaled deeply. Despite the musty smell and the mugginess of a tepid sauna, this was air that had been breathed by Galileo, Einstein, Christ, Mohammed, Ransome, Hitler. The feeling that flooded through her was as close as she had ever come to a religious experience. She opened her mouth to remark on that fact, then choked as a bass croak burst forth from her lips.

Lars, who had been watching her, grinned broadly. It was obvious that he had been expecting it. When he spoke, his own voice had the overtones of a kettledrum.

"Strange, isn't it?"

"What's the matter with our voices?"

"Earth has a nitrogen-oxygen atmosphere."

"So?"

"So, think back to your secondary school physics class. The speed of sound here is a hell of a lot slower than it is at home."

"That's right," she stammered as a horribly low-pitched sound issued from her mouth and a fact from long ago floated into her consciousness. "Vocal chords vibrate at a lower frequency in nitrogen-oxygen, don't they?"

He nodded.

The cloud cities of Saturn used helium in their breathing mixes. They had to. Pure oxygen under the pressure at which the cloud cities floated was both poisonous and highly flammable. Titan mimicked the cloud cities in order to use their atmospheric control equipment. The result was that among the contemporary human race, everyone was a soprano.

"Why didn't you sound any different on the radio?" Kimber asked.

"I'm still using a helium-oxygen mix in my suit. I am about to run out, however, and will have to switch to local air. The switchover means a change to the suit software, so I suspect we'll switch you over with the rest of us."

"Are we going to sound like thisall the time ?""All the time you're breathing Earth standard atmosphere," he said with a grin. "Don't worry, you'll get used to it. Just keep telling yourself that this is what human beings are supposed to sound like."

She grimaced.

"Yeah, I know. I haven't felt like this since my voice changed the first time."

They removed their suit torsos and indulged in an orgy of mutual scratching. Beneath her suit, Kimber wore the usual body stocking of low friction fabric. Already, perspiration stains were appearing at her armpits and down her back. She asked Sands if anything could be done about the temperature inside the laboratory.

"We've got the cooling turned up high. Remember we are fighting a thirty-year heat soak. Still, we gain about three degrees a day. At that rate we ought to be comfortable in relatively short order."

"In the meantime, we sweat!"

"'Fraid so. Come on, I will give you the quick tour. That ought to get your mind off it."

They hung their suits from a variety of pegs jutting from the wall in what had been turned into an impromptu suiting room. Kimber wondered what this area had originally been used for. Lars then led her down a long tunnel lit by widely spaced glow tubes. Kimber recognized the lights. She had helped load them aboard the landing boat two days earlier.

The energy screen laboratory had been laid out as a giant cross, with two subterranean tunnels running several hundred meters at right angles to one another. The intersection of the tunnels had been hollowed out into a large hemispherical cavern. It was in this cavern that they found Halley Trevanon stringing cables.

"Welcome to Hell City!" Halley exclaimed upon seeing Kimber. She was dressed in shorts and a halter, and her hair was matted down with perspiration.

"Thanks, I think."

Halley laughed. "You should have been here yesterday. It was really hot then."

"I'm going to take Kimber to see The Vault," Lars said. "Are the lights still on back there?"

Halley shook her head. "I unplugged them to check out the lights on Broadway. Wait a minute and I'll switch them back."

She unplugged one set of wires from the general tangle and switched them to another. When she was finished, she said, "There. Vault's lit up again."

"Thanks."

"What's this vault?" Kimber asked.

"You'll see," Lars responded cryptically.

He took her by the arm and guided her into the tunnel at right angles to the one they had entered. He warned her to watch her step because the ceiling had fallen in places. They passed a large crack in the tunnel wall where it was possible to feel a hot, wet wind.

"That's one of our problems. We are going to have to find and plug all of those if we are going to makethis place truly livable. That 'we' is you, Halley, and I. The scientists will be too busy sorting through whatever data we find."

Kimber nodded.

Lars continued to lead her down the tunnel past offices, workrooms, and other enclosed spaces whose purpose was not obvious. They reached what appeared at first to be a dead end. Then, as they got closer, Kimber noted that the tunnel was sealed off by a huge hatch. In the moment she saw it, she knew why it had been named "The Vault."

The door was four meters high by six wide, completely filling the tunnel cross-section. It had solidity unknown on Saturn, and only rarely approached on Titan. It was of indeterminate thickness, although to judge by the size of the rusted hinges, it had been designed to withstand considerable force.

"We think their test facilities are behind this," Lars said. "At least, we haven't found them anywhere else.

We'll know as soon as we open it."

"Canwe open it?" Kimber asked dubiously. In addition to the rusted hinges, the giant door's frame was askew, twisted out of alignment as though by a giant hand. That had undoubtedly been done by the earthquakes that had accompanied the boiling of the oceans.

"Not the normal way, that's for sure! On the other hand, we know the Bormans did not get inside. They left a few marks on the door, but didn't come anywhere close to forcing it. Professor LeBlanc is trying to decide whether it would be easier to drill through or to tunnel around. He's arranging to have the equipment we'll need sent down fromVixen ."

Kimber gazed at the massive construct for a few seconds. "I wonder what they were afraid of," she mused.

"Pardon?"

"You build something like this to either keep people out or to keep something else in. I wonder why they went to all the trouble."

"A good question," Lars replied. His eyes were serious as he surveyed the massive barrier. "I think we'd better find an answer before we try to drill our way in."

Professor Paolo Renzi looked at the two neat stacks of glass tiles and smiled. The tiles were the size and shape of dominoes. When held up to the light they sparkled with a rainbow of internal holographic color.

They were holographic storage modules of a type in general use two centuries earlier. Renzi reached out, took one from the smaller of the two piles, and popped it into the receptacle of his modified data reader.

The screen cleared to show the front page of a newsfax. The date at the top was from a time three decades before the flaring sun had forced the Earth's evacuation. Renzi's smile grew even broader as he scanned the tile to discover it filled with other news from the period. He ejected the tile from the reader and added it to the larger of his two piles. As he did so, he thanked whatever gods there were that Factor Crawford had chosen him as leader of the expedition. To miss this opportunity would have been the greatest disappointment of his life.

During their first sweep of the laboratory facilities, the Titanian ground party had discovered nearly two dozen of the tiles. Most had been found in drawers or other out of the way places. Some had dropped behind filing cabinets. So far, the harvest had revealed nothing at all about the operation of the energyscreen laboratory. Most of the modules were mass media recordings of periodicals and newsfaxes.

Despite their lack of bearing on his mission, Renzi considered the tiles an important find. The period of humanity's last century on Earth had long fascinated him. The thought that these record tiles might contain new insights into the period left Renzi anxious with anticipation.

As might have been expected, news that Sol was about to enter a period of long term instability had produced a tidal wave of shock on Earth, Luna, and throughout the space habitats. For a time it had appeared the news would trigger the suicidal tendencies humanity had managed to suppress for more than a century. The peace held ... barely, but the race entered a decade-long dark age. It was a time when societies disintegrated under the strain of rioting, crime, drug use, and a philosophy of unrestrained hedonism. Eventually, however, a hidden strength had emerged from the ruins. Increasingly, people had begun to raise their clenched fists to the traitor star in the sky and shout their defiance. Out of that defiance had come one of the grandest plans ever devised.

For nearly a century, the human race had concentrated on pure scientific research as never before. Any possibility of escaping the flaring sun, no matter how remote, was explored. The period had become known as the Golden Age of Science.

Paulo Renzi had long made the study of those years his avocation. As one who was forever battling for larger budgets and a more resources, Paulo Renzi had long wished that he had been born into an age where these had not been considerations. Nor had the Golden Age been a complete failure. Much good had come out of the striving. Without discoveries in those hectic years, cloud cities would not have been possible.

One result of such research had been a tenfold increase in the scientists' understanding of solar processes. In the end, it had been the solar physicists who had convinced the planetary government that they had no choice but to seek sanctuary in the outer system.

"Still drooling over your tiles, Paulo?" Arthur Linder, the expedition's number two man asked from the open doorway.

Renzi glanced up and grinned at his colleague. "You know me far two well, Arthur. I am afraid it takes all of my willpower merely to scan the data. I want to dive in with both feet."

"How is the catalog coming?"

"Just about done. I'm afraid the information we are really looking for isn't here."

Linder shrugged. "Hardly surprising. The Bormans would have harvested it thirty years ago if it had been easily accessible. If we're going to find anything, it will be in The Vault."

"What progress there?"

"LeBlanc thinks he can cut through in about three days. They are setting up the laser now. I can tell you that Captain McCarver didn't like sending down his spare reactor."

"Can't say I blame him. Still, we have to get through that door. We've swept everything else clean."

Linder pulled up a chair, knit his fingers behind his head, and propped his grimy boots onto the tabletop where Renzi had stacked the tiles. "Sands just reported that he's nearly got the leaks plugged. He should have them done tomorrow. After that, he wants to start working on improving our defenses."

"A waste of time," Renzi muttered."That may be true," Linder responded. "Still, it's orders and we'd best follow them. Just remember, 'It don't have to make sense...'"

"' ... It's government policy,'" Renzi said, completing the quotation that had probably been old when Julius Caesar was in diapers.