"I can offer you Coke, Diet Coke, Fanta or Sprite," Gordon said. They were standing by a dispensing machine in the hallway of the ITC labs.

"I'll take a Coke," Stern said.

The can clunked to the bottom of the machine. Stern took it, pulled the tab. Gordon got a Sprite. "It's important to stay hydrated in the desert," he said. "We have humidifiers in the building, but they don't work well enough."

They continued on down the corridor to the next doorway.

"I thought you might want to see this," Gordon said, taking Stern into another lab. "If only as a matter of historical interest. This was the lab where we first demonstrated the technology." He flicked on the lights.

The lab was a large and untidy room. The floor was covered with gray antistatic tiles; the ceiling above was open, showing shielded lights and metal trays holding thick cables that ran down like umbilicus lines to computers on tables. On one table, there were two tiny cagelike devices, each about a foot high. They were about four feet apart on the table, and connected by a cable.

"This is Alice," Gordon said proudly, pointing to the first cage. "And this is Bob."

Stern knew that by long-standing convention, quantum transmission devices were labeled "Alice" and "Bob," or "A" and "B." He looked at the little cages. One held a child's plastic doll, a girl in a pioneer-style gingham dress.

"The very first transmission occurred here," Gordon said. "We successfully moved that doll between the cages. That was four years ago."

Stern picked up the doll. It was just a cheap figurine; he saw plastic seams running down the side of the face and body. The eyes closed and opened as he tipped it in his hand.

"You see," Gordon said, "our original intention was to perfect three-dimensional object transmission. Three-dimensional faxing. You may know there has been a lot of interest in that."

Stern nodded; he'd heard about the research work.

"Stanford had the earliest project," Gordon said. "And there was a lot of work in Silicon Valley. The idea was that in the last twenty years, all document transmission has become electronic - either fax or e-mail. You don't need to send paper physically anymore; you just send electronic signals. Many people felt that sooner or later, all objects would be sent the same way. You wouldn't have to ship furniture, for example, you could just transmit it between stations. That kind of thing."

"If you could do it," Stern said.

"Yes. And so long as we were working with simple objects, we could. We were encouraged. But, of course, it isn't sufficient to transmit between two stations connected by cables. We needed to transmit at a distance, over airwaves, so to speak. So we tried that. Here."

He crossed the room, and came to two more cages, somewhat larger and more elaborate. They were beginning to resemble the cages Stern had seen in the cave. These cages had no connecting cables between them.

"Alice and Bob, part two," Gordon said. "Or as we called them, Allie and Bobbie. This was our testbed for remote transmission."

"And?"

"Didn't work," Gordon said. "We transmitted from Allie but never got to Bob. Ever."

Stern nodded slowly. "Because the object from Allie went to another universe."

"Yes. Of course, we didn't know that right away," Gordon said. "I mean, that was the theoretical explanation, but who would suspect it was actually happening? It took us a hell of a long time to work it out. Finally, we built a homing machine - one that would go out, and come back automatically. The team called it `Allie-Allie-in-come-free.' It's over here."

Another cage, still larger, perhaps three feet high, and recognizably like the cages that were now used. The same three bars, the same laser arrangement.

"And?" Stern said.

"We verified that the object went out and back," Gordon said. "So we sent more elaborate objects. Pretty soon we succeeded in sending a camera, and got back a picture."

"Yes?"

"It was a picture of the desert. Actually, this exact site. But before any buildings were here."

Stern nodded. "And you could date it?"

"Not immediately," Gordon said. "We kept sending the camera out, again and again, but all we got was the desert. Sometimes in rain, sometimes in snow, but always desert. Clearly, we were going out to different times - but what times? Dating the image was quite tricky. I mean, how would you use a camera to date an image of a landscape like that?"

Stern frowned. He saw the problem. Most old photographs were dated from the human artifacts in the image - a building, or a car, or clothing, or ruins. But an uninhabited desert in New Mexico would hardly change appearance over thousands, even hundreds of thousands, of years.

Gordon smiled. "We turned the camera vertically, used a fish-eye lens, and shot the sky at night."

"Ah."

"Of course it doesn't always work - it has to be night, and the sky has to be clear of clouds - but if you have enough planets in your image, you can identify the sky quite exactly. To the year, the day and the hour. And that's how we began to develop our navigation technology."

"So the whole project changed…"

"Yes. We knew what we had, of course. We weren't doing object transmission anymore - there wasn't any point in trying. We were doing transportation between universes."

"And when did you start to send people?"

"Not for some time."

Gordon led him around a wall of electronic equipment, into another part of the lab. And there, Stern saw huge hanging plastic sheets filled with water, like water beds turned on end. And in the center, a full-size machine cage, not as refined as the ones he had seen in the transit room, but clearly the same technology.

"This was our first real machine," Gordon said proudly.

"Wait a minute," Stern said. "Does this thing work?"

"Yes, of course."

"Does it work now?"

"It hasn't been used for some time," Gordon said. "But I imagine it does. Why?"

"So if I wanted to go back and help them," Stern said, "then I could - in this machine. Is that right?"

"Yes," Gordon said, nodding slowly. "You could go back in this machine, but-"

"Look, I think they're in trouble back there - or worse."

"Probably. Yes."

"And you're telling me we have a machine that works," Stern said, "right now."

Gordon sighed. "I'm afraid it's a little more complicated than that, David."

Kate fell in slow motion as the ceiling stones gave way. As she descended, her fingers closed on the ragged mortared edge, and with the practice of many years, she gripped it, and it held. She hung by one hand, looking down as the falling stones tumbled in a cloud of dust onto the floor of the chapel. She didn't see what had happened to the soldiers.

She raised her other hand, grabbing the stone edge. The other stones would break away any minute, she knew. The whole ceiling was crumbling. Structurally, the greatest strength was near the reinforced line of the groin, where the arches met. There, or at the side wall of the chapel, which was vertical stone.

She decided to try and get to the side wall.

The stone broke away; she dangled from her left hand. She crossed one hand over the other, reaching as far as she could manage, trying again to spread the weight of her body.

The stone in her left hand broke loose, falling to the floor. Again she swung in the air, and found another handhold. She was now only three feet from the side wall, and the stone was noticeably thicker as it swelled to meet the wall. The edge she was holding felt more stable.

She heard soldiers below, shouting and running into the chapel. It would not be long before they were shooting arrows at her.