“I may be the only person in the world who breaks Enigma messages for fun in my spare time,” said Ruthie. “Look—at position 15 the letter ‘P’ lines up with ‘I,’ then at position 26 the letter ‘I’ enciphers as ‘A.’ At position 3 ‘A’ aligns with ‘O,’ at position 21 ‘O’ enciphers as ‘Q,’ and at position 1, ‘Q’ lines up with ‘P’ and we’re back to the original letter and the loop is closed. Now I can program the Bombe.”

“What is this bomb you keep talking about?” said Nemo. “I don’t see how an explosion is going to improve our situation.”

Ruthie glanced at the time on her phone: 1:14 a.m. The night watchman would be in the main house and walking the huts behind it for the next thirty minutes. She could risk turning on the lights. She flipped a switch and the room filled with a cool fluorescent glow. In the center of the space, where Ruthie had already uncovered it, stood a black machine about the size of two large refrigerators. The side facing them was covered with different colored wheels about five inches in diameter each with the letters of the alphabet printed around the front edge. The colored wheels gleamed in the light and the whole contraption seemed, to Nemo, to pulse with mystery and potential.

“This,” said Ruthie, “is the Bombe.”

“Alan Turing designed the Bombe starting with work done by the Poles,” said Patton as Ruthie began fiddling with wires at the back of the machine.

“And then,” said Ruthie, “Gordon Welchman came up with the idea of the diagonal board and that meant . . . You have no idea what I’m talking about, do you?”

“Can this thing break the code?” said Nemo.

“This machine won the war,” said Ruthie.

“But can it decode our message?” said Nemo.

“Not entirely,” said Ruthie. “But if I set it up correctly, using Patton’s crib and the loop we found, it can reduce the number of possible settings for the Enigma machine that encoded this message from one hundred and fifty trillion to about six hundred or so. The rest is fairly easy to do by hand.”