“And Carruthers didn’t say anything about doing anything before he followed you?” Warder asked. “Checking on something?”

He shook his head. “He said, ‘I’m right behind you.’ ”

“Was there anyone about?”

He shook his head again. “The sirens had gone. And there’s nobody living in that part of the city. It’s all burnt down.”

“The sirens had gone?” Warder said. “Were you under attack? Could a bomb have hit—” She looked up suddenly and saw me. What are you doing here?” she said. “What happened to Kindle?”

“Advanced time-lag, thanks to you people,” I said, flailing my way out of the veils. “Where’s Mr. Dunworthy?”

“Over at Corpus Christi with the forensics expert,” she said.

“Go tell him I’m here and need to talk to him now,” I said to the new recruit.

“I’m trying to find out what happened to Carruthers,” Warder said, flushing angrily. “You can’t just come in here and—”

“This is important,” I said.

“So is Carruthers!” she snapped. She turned to the new recruit. “Were there any delayed-action bombs in the area?”

The recruit looked uncertainly from her to me. “I don’t know.”

“What do you mean, you don’t know?” Warder said angrily. “What about the buildings and ruins in the area, were they unstable? And don’t tell me you don’t know!”

“I’d best go fetch Mr. Dunworthy,” the recruit said.

“All right,” Warder snapped. “Come straight back. I’ve some more questions to ask you.”

The recruit made his escape, brushing past T.J., who was on his way in with a stack of books, vids, and disks. “Oh, good,” he said when he saw me. “I want to show you both—” He stopped, looking round. “Where’s Verity?”

“In 1888,” I said. “She got time-lagged doing all those drops for you.”

“They didn’t turn up anything,” he said, trying to set the stack down without it falling over, “which doesn’t make any sense. There’s got to be increased slippage around the site. Here, let me show you.”

He started to lead me over to the comp setup and then stopped and went over to the console and asked Warder, “Was there slippage on Ned’s drop?”

“I haven’t had time to calculate it,” Warder said. “I’ve been trying to get Carruthers out!”

“Okay, okay,” T.J. said, holding up his hands defensively. “Could you please calculate it?”

He turned to me. “Ned, I want to show you—”

“What’s this about slippage on my drop?” I said. “There isn’t any slippage on return drops.”

“There was on Verity’s last drop,” he said.

“What’s causing it?”

“We don’t know yet,” he said. “We’re working on it. Come here. Let me show you what we’re doing.” He led me over to the comp setup. “Did Verity tell you about the Waterloo sims?”

“More or less,” I said.

“Okay, it’s very hard to make an accurate comp model of an historical event because so many factors are unknown, but Waterloo’s an exception. The battle’s been analyzed and every incident’s been described down to a microscopic level. Also,” he said, his black fingers typing rapidly, “it has several crisis points and a number of factors which could have made the battle go either way: the violent rainstorms on the sixteenth and seventeenth, General Grouchy’s failure to come up—”

“Napoleon’s bad penmanship,” I said.

“Exactly. Napoleon’s message to D’Erlon and the failure to take Hougoumont, among others.”

He hit more keys, leaning round to see the bank of stack screens behind him.

“All right, here’s what we’ve been looking at,” he said, picking up a lightpen and walking over to the center screen. “This is a sim of Waterloo as it actually happened.”

The screen showed a three-dimensional gray blur with lighter and darker areas. “This is the battle,” he said, switching on the pen and pointing it into the center of the three-dimensional blur. “And here,” he pointed at the edges, are the surrounding temporal and locational areas the battle affected.”

The light darted back to the center and rapidly pointed to several places. “Here you can see the battle at Quatre Bras, the fight for Wavre, the charge of the Old Guard, the retreat.”

I couldn’t see anything but assorted gray blurs. I felt the way I always do when a doctor shows me a scan. “Here you see the lungs, the heart—” I never see anything of the sort.

“What I’ve done is introduce simulated incongruities into the model and see how the sim changes,” he said.

He moved to the screen on the left. As near as I could tell, it looked identical to the one in the center. “In this one, for example, Napoleon sent an illegible order to D’Erlon to turn toward Ligny, with the result that he brought his men up behind Napoleon’s left flank instead of ahead of it and was mistaken for the enemy. I introduced a simulated historian here,” he said, pointing at gray, “who substituted a legible order for Napoleon’s note, and as you can see, it changed the picture radically.”

I would have to take his word for it.

“When the incongruity’s introduced, you get a pattern of radically increased slippage at the site,” he pointed with the lightpen, “and then slightly lower levels here and here surrounding the site, and then smaller peripheral patches as the system corrects itself.”

I squinted at the screen, trying to look intelligent.

“In this case, the system was able to self-correct almost immediately. D’Erlon issued the orders to his second-in-command, who gave them to a lieutenant, who couldn’t hear him for the artillery fire, and sent the troops up on the left flank after all, and the situation reverted to its original pattern.”

He pointed the lightpen at the top row of screens. “I tried a number of variables of varying severity. In this one, the historian breaks the lock on the gate at Hougoumont. In this one, he spoils an infantryman’s shot so Letort isn’t killed. In this one here, the historian intercepts a message between Blücher and Wellington,” he said, pointing at one screen after another. “They vary greatly in their impact on the situation and in how long it takes the continuum to self-correct.”

He pointed at more screens. “This one took a few minutes, this one took two days, and there doesn’t seem to be a direct correlation between the seriousness of the incongruity and its consequences. In this one,” he pointed at the far left bottom screen, “we shot Uxbridge to prevent his suicidal charge, and his second-in-command immediately took up the charge with the same result.

“On the other hand, in this one,” he indicated a screen in the second row, we had an historian dressed as a Prussian soldier stumble and fall during the fight for Ligny, and the self-correction was enormous, involving four regiments and Blücher himself.”

He moved to a screen in the center. “In this one, we changed the circumstances at La Sainte Haye. The thatched roofs caught fire from the artillery shells, and a chain of men with soup kettles full of water managed to put the fires out.”

He pointed at a spot near the center. “I introduced an historian here to steal one of the soup kettles. It created a major incongruity, and the interesting thing is that the self-correction didn’t just involve increased slippage here and here,” the light pointed at the top of the screen, “but here, before 1814.”

“It went back in the past and corrected itself?”

“Yes,” he said. “In the winter of 1812, there was a bad snowstorm, which caused a deep rut in the road in front of La Sainte Haye, which caused an oxcart passing over it to lose part of its load, including a small wooden keg full of beer, which a servant found and carried home to La Sainte Haye. The keg, with the top hacked off, was substituted for the missing soup kettle in the bucket brigade, the fires were put out, and the incongruity was repaired.”

He went back to the comp, hit more keys, and brought up a new set of screens. “This one, where Gneisenau retreats to Liege, and this one, in which the historian helps push a cannon out of the mud, show self-corrections in the past, too.”