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“Tea next week with your family, then, before I leave.” Francis passed his thumb over her knuckles. “D’you want a ring?”

“Yes,” she heard herself laugh. “I want a ring.”

“Bound to be a ruby somewhere in London that matches your lips.” He let go of her hand, backed up toward the little fleet of cars. The prime minister had already climbed inside and his chauffeur was starting up; the aides hovered by the next vehicle, waiting for their driver. Francis looked at Mab another long moment, the curtains still swept aside from his naked gaze. No one had ever looked at Mab like that in her life.

Her fiancé climbed into the car. It moved off, and Mab walked, still in a daze, back toward her hut. Mab Gray, she thought. Mrs. Gray.

Mab saw Winston Churchill’s face turned out the window of the lead car as it swept around the drive toward the gates. She put up her hand and flashed a V with two fingers, his famous sign. V for victory. Because today she’d won, damn it. She’d won.

The prime minister put a hand out the window and flashed a V back.

Chapter 28

FROM BLETCHLEY BLETHERINGS, OCTOBER 1941

Preoccupied”—adjective, “engrossed in thought.” Taken to an entirely new level by BP personnel, who are frequently too preoccupied to notice if they have put their knickers on backward, if the prime minister has dropped in for tea, or if everything except the pencil actually in their hand is on fire.

Beth missed everything that autumn. Churchill’s visit, Mab’s engagement—it all passed Beth in a blur. “Honestly, where do you Cottage girls go?” Osla demanded. “The blinking moon?”

Beth just stared, exhausted. She was sleeping very badly—at night her brain roiled so much with five-letter groups and quartets of wheels, she was lucky if she got more than a few hours of tossing and turning. Boots had given up sleeping on her feet and retired in disgust to the basket on the floor.

“MI-5 manages the controlled German agents,” Dilly had mused aloud at the beginning, with his usual complete disregard for Bletchley Park’s paranoia about keeping its workers in the dark. “MI-5 makes them send out false information on their own wireless transmitters, as directed by our case officers, using their own hand cipher given to them by the Germans. Their controllers are usually in Lisbon, Madrid, or Paris; they analyze everything before transmitting to Berlin. We just need to crack the one they use to make sure Berlin is swallowing it . . .”

But “just” hadn’t happened yet, even though Dilly’s entire section had been banging their brains against it for three months so far. This wasn’t like the three-day sprint they’d flung themselves into to break the Matapan battle orders—excruciating but finite. This was a desperate, endless slog of dead ends, going down one promising path until it petered out, then trying another. With no time for recovery or rest.

“If I analyze the hand-cipher traffic from the individual network, we should get some good cribs,” Dilly muttered, but he’d been analyzing the traffic all this time and nothing consistent came up. With Italian naval Enigma, cribs gave you something to rod for. Here they had nothing. It was those damned four wheels used in the Abwehr Enigma, turning over much more frequently with no predictable pattern.

Have to crack it, have to crack it. Her entire body was tense as wire, and she was so far down the rabbit hole she felt like screaming. If she screamed, she’d probably scream in five-letter clumps. Have to crack it.

Beth wasn’t going anywhere except the Cottage, where she overstayed her shifts and barely came home in time to walk Boots before being hauled into the kitchen. Then she’d stand stirring rice pudding over the heat, watching boxing chains unspool in her head until her mother had her by the elbow, shaking her. “Bethan, you’ve burned it—”

Five minutes later Beth would realize she’d gone sideways in her thoughts all over again, not listening to a word of the lecture. Sometimes she managed to mumble, “I’m sorry, Mother, what were you saying?”

And Mrs. Finch would walk away quivering with anger, saying, “I think you’re going mad, I really do!”

I think so too, Beth sometimes thought.

Dilly burst into the Cottage one interminable night shift, waving his glasses. “Lobsters!”

Beth traded looks with Phyllida at the next desk. “Lobsters?” When Dilly was in one of his Catherine wheel moods and started firing ideas off like sparks, it was best to patiently ask questions until he started making sense. Peggy was better at it than Beth, who knew she wasn’t making much sense these days herself. Only yesterday she’d noticed the big ruby glinting on Mab’s hand, and said, “How long have you had that?” Mab had looked at her a little strangely and said, “A month, Beth. Francis gave it to me before he went overseas. After I took him to meet Mum and Lucy.”

“After there was that tempest in a teapot the high-ups made about the new Agatha Christie book?” Osla had prompted when Beth looked blank. “Don’t tell me you forgot that, too!”

Beth had, apparently. And now she was being asked to think about lobsters.

“The moment all four wheels in the machine turn over between the first two letters of the indicator and again in its repeat position—think of that as a crab.” Dilly waved four fingers like crab legs all moving together.

“It’s not a way into the cipher.” Beth poured cold coffee into a cup and pushed it into his hand.

“But if there are four-wheel turnovers on both sides of the throw-on indicator key-block, there could be more turnovers on one side of the key-block alone. Think of that as a lobster . . .” He made lobster claw gestures, spilling coffee, jabbering as Beth listened. Nothing made sense, but she was used to Dilly’s Lewis Carroll logic by now and found her brain diving down the right angle he’d just proposed.

“If we could find your lobster,” she said slowly, “and a long block of text after it, maybe we’d have better luck breaking key-blocks of indicators on the same setting . . .” She didn’t really know where she was going with that yet, but the best way to find out was to have a go, as Dilly always said. Beth pulled out the pencil stub holding her knotted-up hair. “Let’s go lobster hunting.”

It took four days to find a message with the right turnover, but as soon as Beth had it, numbers started spiraling and chaining madly. “Yes,” she yelped in the middle of the day shift. “Give me a cipher letter pairing in position one, I can chain together some deductions about the other pairings . . .” Her words tumbled madly. “Don’t you see?” she finished in a rush, blood fizzing.

Phyllida rubbed the bridge of her nose. “Sort of.”

Peggy peered closer. “Show me.”

“Where’s Dilly?” Beth looked around. “Did he go home?”

“Yes, he did.” Peggy’s face was drawn. “And we aren’t bothering him. Show me . . .”

It had gone October, trees flaming yellow and orange around the lake, by the time Beth could crack one wheel setting. November frosts had hardened the ground before the Cottage girls could theorize how often the German technicians, when they picked four-letter wheel settings for the day’s traffic, fell back on particular words: NEIN, WEIN, NEUN . . . “Four-letter names, too,” Peggy mused.

Then Beth broke a wheel setting on some Balkan-based traffic after she broke S-A for the two right-hand wheels, and made a grainy-eyed, dawn-hour guess that the Balkan operator had a girlfriend named ROSA. With R and O fixed in position, everything fell into place; generated alphabets of text and cipher could then be swiftly buttoned up, and lists of four-letter German names and words were soon pinned up on every Cottage wall.

“We’re getting there,” Dilly encouraged, sprinkling tobacco all over Beth’s work. “It’s coming, ladies.”

In early December, the moment came. Everyone clustered around Beth’s desk, barely breathing as she pulled blocks of German out of the chaos. There it was, a decrypted message—the German-speaking women confirmed it was legible. Beth didn’t ask or care what it said. She put her knuckles to her mouth and bit down savagely, little dying fragments of code spasming across her vision. She was suddenly hungry and didn’t know when she’d last eaten, didn’t know when she’d last been home or what day it was. She didn’t know anything except that she’d done it. They’d all done it. They’d broken the Spy Enigma.

Peggy swayed where she stood at Beth’s shoulder. She put her head in her hands, and suddenly the silence snapped. Phyllida threw herself into the arms of the puzzled tea lady, who had just trundled in with fresh chicory coffee. Several girls laughed as if they were drunk, several cried, all so finely balanced between elation and exhaustion they couldn’t speak a single coherent word.