than five hundred others, and Michael couldn’t see how that couldn’t have caused changes, so we began looking for discrepancies.”
“And did you find them?” he asked.
“None that I could determine for certain were discrepancies,” Polly said, “but Michael wasn’t the only one who’d done something. Eileen—Merope—stopped two of her evacuees from sailing on the City of Benares, and I was responsible for a shopgirl’s being injured and nearly killed. But we didn’t know it was possible to alter the course of events. We thought the slippage kept historians from—”
Mr. Dunworthy shook his head. “We were wrong about the slippage’s function. It wasn’t a line of defense guarding against damage we might do to the continuum.
It was a rearguard action against an attack that had already happened—an attempt to hold a castle whose walls had already been breached.”
“By time travel,” Polly said.
“By time travel. And in most cases over the years, the defenses were sufficient to hold the castle. But not all. It couldn’t hold it against multiple simultaneous attacks or in instances where the breach was at a particularly vital spot—”
Like Dunkirk, Polly thought. Or the autumn of 1944, when the lightest touch of a Spitfire’s wing on a V-1’s fin could change who lived and who died.
“Or in instances where the initial breach was too great,” Mr. Dunworthy was saying. “In those cases, no amount of slippage would have been sufficient to prevent the enemy from breaking through, so the only thing the continuum could do was to attempt to isolate the infected area—”
Like Eileen’s quarantine.
“—and attempt to repair the damage.”
“To shut down access to the past,” Polly said, “which is what you think the continuum did.”
He nodded. “Trapping you here.”
And you. “I’m so sorry, Mr. Dunworthy.”
He shook his head. “You are not to blame.”
“But if I’d told you I’d done the rocket attacks first,” she said. “I knew you were canceling drops and changing schedules, even if I didn’t know the reason. I was afraid you’d cancel mine, so I didn’t report in, and I made Colin promise he wouldn’t tell you.”
He nodded as if he wasn’t surprised. “Colin would do anything for you,” he said.
“Oh, this is all my fault! If I hadn’t made him promise, if I’d reported in, you wouldn’t have let me come. You wouldn’t have had to come after me—”
“No, you don’t know the whole story,” he said, putting up his hand to stop her. “There was an increase in slippage even before you went to 1944, but it wasn’t large, and I didn’t think it was serious. The amount of slippage had often been greater than the circumstances seemed to merit, and at other times far less, and I thought there was a simpler explanation than the one Ishiwaka had arrived at, even after he showed me his equations. I certainly didn’t see any need to pull out my historians and shut down all time travel. I thought canceling the drops of historians with deadlines and putting the others in chronological order was sufficient till I had more data, but Dr. Ishiwaka was right. I should have pulled you all out.”
“But you couldn’t have known what the increase meant—”
“Dr. Ishiwaka had told me exactly what it meant, but I refused to believe him. We’d been traveling to the past for forty years without incident. I found it impossible to believe that we were a danger to the course of history. I should have listened to him. If I’d pulled you out, Michael Davies would still be alive, and you and Merope
—”
“Merope?” she said, alarmed. “She doesn’t have a deadline. This was her first assignment. Wasn’t it?”
“Yes,” he said, and she knew there was still more.
“The shutdown might not be a result of the continuum’s attempt to correct itself,” he went on. “It might be some sort of reflexive response to the damage, like shock in a trauma patient. And even if it is an attempt at self- correction, there’s no guarantee it will be successful. The damage may be too great or too widespread to be repairable.”
“But it’s not,” Polly said. “We didn’t lose the war. I was at VE-Day—”
“That was before Michael saved the soldier, and you and Merope—”
“I know, but Merope was there, too. I saw her. And she hasn’t gone yet. She went there—will go there after Mike saved Hardy and we did all the other things, so they can’t have affected the outcome of the war.”
But Mr. Dunworthy was shaking his head. “At the point when you saw her, there would still have been a VE- Day to which she could go. The course of history—
past and present—would have remained as it had always been until the alterations reached a tipping point. That is why we are able to be here, even though we’re part of that unaltered future. And why Eileen could have gone to VE-Day. It would have remained unaltered until the moment the final alteration occurred and the continuum could not correct for it—”
“And then everything would change.”
“Yes.”
“But you said …” She frowned, trying to grasp it. “I don’t understand. Hadn’t that tipping point already happened? The drops had stopped working.”
“Not entirely. Mine was still working in mid-December.”
