Patton racked her brain trying to remember everything she had learned about cracking Enigma at that summer course at Harvard years ago. Mostly she remembered the cute English girl who sat at the desk next to hers. Ruthie’s accent had almost made Patton swoon the first time she heard it. And Ruthie had the same enthusiasm for Alan Turing’s work that Patton did. Ruthie told Patton the end of Turing’s story—that he had been prosecuted for homosexuality, sentenced to chemical sterilization, and subsequently committed suicide. Patton had been horrified that such a brilliant man, who had been so essential in the defeat of Nazism, had been treated so inhumanely. But for that month at Harvard, she didn’t dwell on Turing’s fate. She dwelled mostly on Ruthie, whose lips had been soft and who had been innocent, at least at the start of the course. It had been a lovely summer—nothing serious but lots of fun. But soft lips and an English accent and lost innocence had also distracted Patton from paying attention to the coursework. Luckily, Ruthie had known more about Enigma than the professor did, and Patton could recall lying together on a narrow dormitory bed, the warm summer air wafting in the open window and carrying a hint of the sea, while Ruthie told her about cribs and loops and menus, about programming the Bombe and using the checking machine. Such pillow talk. But Patton had learned more on those nights with Ruthie’s soft body pressed against hers than she did in the classroom during the day.

She copied out the encrypted text from the aging sheet of SS stationery onto the first page of a Moleskine notebook. Nemo had given her some cash to shop for necessities at the airport—the notebook, pencils, and a German phrase book from the bookstore in the international terminal. She examined Jasper’s paper closely, in case it held any other hints, but all she could see in the dim light of the plane was the printed heading “SS H-Sonderkommando” and the barely visible words “Projekt Alchemie.” That, surely, was the place to start. If that phrase appeared near the start of the message and she could guess another word or two, she might come up with a workable crib.

The Allies trying to crack Enigma took advantage of the one weakness in the machine the Nazis used to encode their messages—Enigma never encoded a letter as itself. So, if she compared a possible crib to the cipher text and any of the letters matched, the crib was wrong. What else had Ruthie told her?