"By a narrow definition, that's right," said Tagiri.

"Slavery is when a human being is made property. When one person is able to buy and sell, not just someone's labor, but his actual body, and any children he has. Movable property, generation after generation." Kemal looked at them, at the coldness still visible in their faces. "I know that you all know this. But what you seem not to realize is that slavery was not inevitable. It was invented, at a specific time and place. We know when and where the first person was turned into property. It happened in Atlantis, when a woman had the idea of putting the sacrificial captives to work, and then, when her most valued captive was going to be sacrificed, she paid her tribal elder to remove him permanently from the pool of victims."

"That's not exactly the slave block," said Tagiri.

"It was the beginning. The practice spread quickly, until it became the main reason for raiding other tribes. The Derku people began buying the captives directly from the raiders. And then they started trading slaves among themselves and finally buying and selling them."

"What an achievement," said Tagiri.

"It became the foundation of their city, the fact that the slaves were doing the citizens' duty in digging the canals and planting and tending the crops. Slavery was the reason they could afford the leisure time to develop a recognizable civilization. Slavery was so profitable to them that the Derku holy men wasted no time in finding that the dragon-god no longer wanted human sacrifices, at least for a while. That meant that all their captives could be made into slaves and put to work. It's no accident that when the great flood destroyed the Derku, the practice of slavery didn't die with them. The surrounding cultures had already picked it up, because it worked. It was the only way that had yet been found to get the use of the labor of strangers. All the other instances of genuine slavery that we've found can be traced back to that Derku woman, Nedz-Nagaya, when she paid to keep a useful captive from being fed to the crocodile."

"Let's build her a monument," said Tagiri. She was very angry.

"The concept of buying and selling people was invented only among the Derku," said Kemal.

"It didn't have to be invented anywhere else," said Tagiri. "Just because Agafna built the first wheel doesn't mean that someone else wouldn't have built another one later."

"On the contrary. We do know that slavery -- commerce in human beings -- was not discovered in the one place where the Derku had no influence," said Kemal. He paused.

"America," said Diko.

"America," said Kemal. "And in the place where people weren't conceived of as property, what did they have?"

"There was plenty of bondage in America," said Tagiri.

"Of those other kinds. But humans as property, humans with a cash value -- it wasn't there. And that's one of the things you love best about your idea of stopping Columbus. Preserve the one place on earth where slavery never developed. Am I right?"

"That's not the primary reason for looking at Columbus," said Tagiri.

"I think you need to look again," said Kemal. "Because slavery was a direct replacement for human sacrifice. Are you actually telling me that you prefer the torture and murder of captives, as the Mayas and Iroquois and Aztecs and Caribs practiced it? Do you find that more civilized? After all, those deaths were offered to the gods."

"You will never make me believe that there was a one-for-one trade, slavery for human sacrifice."

"I don't care whether you believe it, " said Kemal. "Just admit the possibility. Just admit that there are some things worse than slavery. Just admit that maybe your set of values is as arbitrary as any other culture's values, and to try to revise history in order to make your values triumph in the past as well as the present is pure--"

"Cultural imperialism," said Hassan. "Kemal, we have this argument ourselves every week or so. And if we were proposing to go back and stop that Derku woman from inventing slavery, your point would be well taken. But we aren't trying to do anything of the kind. Kemal, we aren't sure we want to do anything! We're just trying to find out what's possible."

"That's so disingenuous it's laughable. You've known from the beginning that it was Columbus you were going after. Columbus you were going to stop. And yet you seem to forget that along with the evil that European ascendancy brought to the world, you will also be throwing away the good. Useful medicine. Productive agriculture. Clean water. Cheap power. The industry that gives us the leisure to have this meeting. And don't dare to tell me that all the goods of our modern world would have been invented anyway. Nothing is inevitable. You're throwing away too much."

Tagiri covered her face with her hands. "I know," she said.

Kemal had expected argument. Hadn't she been sniping at him all along? He found himself speechless, for a moment.

Tagiri took her hands away from her face, but still she looked at her lap. "Any change would have a cost. And yet not changing also has a cost. But it's not my decision. We will lay all our arguments before the world." She lifted her face, to look at Kemal. "It's easy for you to be sure that we should not do it," she said. "You haven't looked into their faces. You're a scientist."

He had to laugh. "I'm not a scientist, Tagiri. I'm just another one like you -- somebody who gets an idea in his head sometimes and can't let it go."

"That's right," said Tagiri. "I can't let it go. Somehow, when we're through with all our research, if we have a machine that lets us touch the past, then there'll be something we can do that's worth doing, something that will answer the ... hunger ... of an old woman who dreamed."

"The prayer, you mean," said Kemal.

"Yes," she said defiantly. "The prayer. There is something we can do to make things better. Somehow."

"I see that I'm not dealing with science, then."

"No, Kemal, you're not, and I've never said so." She smiled ruefully. "I was shaped, you see. I was given the charge to look at the past as if I were an artist. To see if it could be given a new shape. A better shape. If it can't, then I'll do nothing. But if it can ..."

Kemal was not expecting such frankness. He had come expecting to find a group of people committed to a course of madness. What he found instead was a commitment, yes, but no course, and therefore no madness. "A better shape," he said. "That really comes down to three questions, doesn't it. First is whether the shape is better or not -- a question that's impossible to answer except with the heart, but at least you have the sense not to trust your own desires. And the second question is whether it's technically possible -- whether we can devise a way to change the past. That's up to the physicists and mathematicians and engineers."

"And the third question?" asked Hassan.

"Whether you can determine exactly what change or changes must be made in order to get exactly the result you want. I mean, what are you going to do, send an abortificant back and slip it into Columbus's mother's wine?"

"No," said Tagiri. "We're trying to save lives, not murder a great man."

"Besides," said Hassan, "as you said, we don't want to stop Columbus if by doing so we'd make the world worse. It's the most impossible part of the whole problem -- how can we guess what would have happened without Columbus's discovery of America? That's something the TruSite II still can't show us. What might have happened."

Kemal looked around at the people who had gathered for this meeting, and he realized that he had been completely wrong about them. These people were even more determined than he was to avoid doing anything foolish.

"That's an interesting problem," he said.