The woman spoke first: "We are not aliens from another planet. We are aliens from earth. We come from five hundred years in your future."

The man continued: "It was the largest engineering enterprise in the history of humanity. The energy we displayed approaching you was only a small fraction of what was required to bend s.p.a.ce and time and send us back. That required the total destruction of a small star, the kind you call a brown dwarf."

"We bring a message of hope and caution," the woman said. "The message of hope is that we are here, and therefore you do have a future. Knowing that is going to change you. The catastrophic war that seems about to begin will evaporate-and a series of things will happen, starting today, that will make war impossible within the lifetimes of most people now living."

"It's been decided," the man said, "that we cannot-and we know from historical record that we did not-tell you what these things are. You have to find them out for yourselves. Experience them as they happen."

"This has never been done before," the woman said. "We have to a.s.sume that so long as the two of us conform to historical record, subsequent events will occur as our history books record them, and there will be peace. But history does not allow us to remain with you, visitors from an impossible time."

The man gestured at the s.p.a.ceship. "Likewise, we have to dispose of the s.p.a.cecraft. If one country took possession of the ship's secrets, it would dominate the world."

The ship had reached the end of the runway. It pivoted slowly and then started to roll back toward them, the hiss of exhaust building to a scream. It was already airborne as it pa.s.sed the reviewing stand, and it arced upward into a vertical climb with such acceleration that within seconds it was a dot, and then it disappeared. Then it exploded, a brilliant perfect sphere of light, in total silence, outside the atmosphere.

"Now there is only one artifact from the future, besides our clothing," the woman said. She held up an ordinary data crystal, and stepped forward to hand it to a technician surrounded by cameras. "Show this a few minutes from now."

"Of course, we are both also artifacts from the future," the man said, "though we're just people." The woman joined hands with him. "You have many ways to extract information from us."

"There was no way," the woman said, "to make us not know things that might be potentially dangerous to your survival."They looked into each other's eyes and said in unison, "So, good-bye." They both slumped to the floor.

The next few minutes were a fast confusing drama of swarming medics, stretchers, helicopters, but Rory hardly noticed it, lost in thought.

She saw what Pepe had meant. Sure, it was a hoax, audacious and mind-bendingly expensive. But of course she wouldn't blow the whistle. There was a big chance it might work; it might become a self-fulfilling prophecy. So long as the secret was kept.

All she wanted to know was how they managed it; how could they put all the pieces together without somebody spilling the beans? Who was in on it? Certainly not fools like Davis.

She watched the crystal the "dead" woman had handed the technician, and it indeed showed their landing, speech, and "death." At least she hoped that was part of the ch.o.r.eography, and they hadn't called upon two people to sacrifice their lives to make the hoax more realistic. The introduction to the scene was convincingly futuristic to her eyes and ears; the voice-over with an unearthly accent, the beginning and ending shots showing a planet of peace and plenty. Cities floating in the air over forests and fields restored to nature. But then the throwaway s.p.a.ceship showed how big a budget they'd had to play with.

The sun was breaking through the clouds, a rare thing, everybody off the roads. She decided to take a walk. Go up to the astronomy building and see what happens. Maybe reckless, but she had a feeling that the government was going to be a little too busy to pick on her for a while.

The building was deserted. Everyone was probably down at the Cape.

Pepe's office was still unlocked. Feeling a little bit guilty, voyeuristic, she went in to snoop around.

On a worktable under the window there were three neat stacks of paper, the last a.s.signments and finals for Pepe's three cla.s.ses.

There was a letter to his secretary, detailing the disposition of these papers, thanking her, and saying good-bye. He would be in touch.

Rory had a feeling that he would not be.

Coda In a quiet corner of Barcelona, the man who was not Pepe Parker relaxed in a situation of modest wealth and perfect privacy. He had a cook, a servant, and a gardener, and walls of books in various languages.

Buried in the bas.e.m.e.nt, there was a weapon that would turn a man into a torch.

With his full white beard and darkened skin, no one would connect him with the youthful Cuban scientist who had run the Coming Committee and mysteriously disappeared.

He spent most of his time reading, in the garden when it was fine, or in front of the fire when it was cool. Sometimes he dined out with beautiful women who thought he was a retired scholar, independently wealthy. Which was true, as far as it went.

In a safe-deposit box at Banco Nacional de Catalunya, there was a single sheet of paper which only he could read. It had a schedule of conservative stock purchases, and the names of the winners of the Kentucky Derby for the next fifty years.