“In which case the retrieval team won’t be either. I think they’re much more likely to read personal ads. There are lots of ‘losts.’ Perhaps we could do something with that.”

“Like ‘Lost: historian. Reward for safe return’?”

“No,” Polly said, “but we could say we’d lost something and give our name and address. Here’s one. ‘Lost: pair of brown carpet slippers on Northern Line platform, Bank Station. If found—’ ”

“Oh,” Eileen said. They looked inquiringly at her. “You told me to remember any detail, no matter how irrelevant, about my conversations with Gerald—”

“Does Gerald’s airfield have the word ‘bank’ in it?” Mike asked eagerly, grabbing for his list of names. “Glaston Bank?”

“No, not that part. The bit about the slippers.”

They looked blankly at her.

“ ‘Slippers’ sounds like ‘slippage.’ ”

“Slippage?”

“Yes. Linna was on the phone while I was talking to Gerald, and whoever she was talking to wanted to know how much slippage there was on someone’s drop, and then when I went through to Backbury, Badri was talking to someone about an increase in slippage, and Linna asked me if the slippage the last time I went through had increased from the other times.”

“And had it?” Mike asked.

“No, and when I told her that, she said, ‘Good,’ and looked at Badri.”

“Who was she talking to, do you know?”

“No. I assume it was Mr. Dunworthy. She called him sir.”

“And it was an increase?” Mike asked eagerly. “Not a decrease? You’re sure?”

“Yes. Why?”

Because then there wasn’t too little slippage, Polly thought. And it couldn’t have let Mike—or me—go to a place where we could alter events.

“They questioned Phipps on his slippage, too,” Mike said. “Did they say anything to you about it when you came through, Polly?”

“They asked me to note how much there was and tell them when I reported in.”

“And how much was there?”

“Four and a half days. It was only supposed to be an hour or two. I assumed there was a divergence point that—”

“I don’t think so,” Mike said excitedly. “I think a bunch of drops were experiencing an increase in slippage, and it was enough to worry them. Which means it couldn’t have been a few days’ worth. It must have been weeks. Or months.”

“And that’s why our retrieval teams aren’t here?” Polly said. “Because the slippage sent them to November or December instead?”

He nodded.

“So all we need to do is wait for them to come fetch us?” Eileen said eagerly.

“No. It might be a while before they get here, and in case you haven’t noticed, this is kind of a dangerous place. The sooner we can find a working drop and get out of here, the better.”

“But if there’s slippage, then Gerald’s drop won’t open either, will it?” Polly asked.

“Even if it doesn’t, he may know more about what the slippage problem is and how long we’re looking at. That means finding him’s still our first priority. And our second’s to make sure the retrieval team can find us when they get here. Eileen, have you had a letter from Lady Caroline?”