Then how am I supposed to find out if Gerald’s there? he wondered. “What if Gerald’s one of the people living on the estate?” he asked.

“He won’t be. That was mostly the top codebreakers, like Dilly Knox and Alan Turing. Turing was Ultra’s computer genius.” She was looking critically at him. “You haven’t any other clothes, have you?”

“No, these are the best I’ve got. Aren’t they good enough?”

“They’re too good. If you’re going as a cryptanalyst—that’s what they called the codebreakers—you’ll have to look the part. Don’t worry, we’ll find you something.”

The “something” turned out to be a secondhand tweed jacket with patches at the elbows, a scruffy-looking wool vest, and a tie with a large grease spot on it. “Are you sure this is what they wore, Polly?” Mike asked doubtfully.

“Positive, although the waistcoat may be too nice.”

“Too nice?”

“These are physicists and mathematicians we’re dealing with. Can you play chess?”

“No. Why?”

“There weren’t enough cryptanalysts in England at the beginning of the war, so they recruited anyone they thought might be good at decoding—statisticians and Egyptologists and chess players. If you could play, it would make a good conversational opening.”

“I could teach you,” Eileen said.

“There isn’t time,” he said. “I want to leave tomorrow.”

“No, you need to wait till Sunday,” Polly said. “It’ll be less conspicuous. Lots of BPers will be coming back from the weekend then. And I need to prep you.”

She did, telling him everything she knew about Bletchley Park and Ultra and the principal players in such detail that he wondered if she was still worried about his altering events, too, in spite of his reassurances. She even told him what the various codebreakers looked like.

So I can keep out of their way, he thought. Which wasn’t a bad idea, just in case. He memorized the names she gave him: Menzies, Welchman, Angus Wilson, Alan Turing.

“Turing’s blonde, medium height, and stammers. Dilly Knox—he heads up the main team of cryptanalysts—is tall and thin and smokes a pipe. And he’s absent-minded. He’s been known to fill his pipe with bits of his sandwich. Oh, and he’s usually surrounded by young women. Dilly’s girls.”

“Dilly’s girls?”

“Yes. They played a vital role in the decoding. They searched through millions of lines of code, looking for patterns and anomalies.”

“How do you know all this?” he asked. A horrible thought struck him. “You didn’t do an assignment at Bletchley Park, did you?” If she had, and she had a deadline …

“No,” she said. “I considered it, but after I’d researched it, I decided the Blitz might be more exciting.”

Not if historians can alter the course of the war, he thought.

On Sunday Polly and Eileen went to the station to see him off and to give him last-minute instructions. “The Park’s in walking distance of town,” Polly said, “but I don’t know in which direction, and asking might look suspicious.”

“I won’t ask,” he assured her. “I’ll find a likely prospect and follow him when I get off the train.”