“Ladies,” said Harold Whoever, “meet the bombe machines.”

They were bronze-colored cabinets, massive things at least six feet high. The front held rows of circular drums, five inches in diameter, letters of the alphabet painted round each one. In this dark hut they loomed like trolls under bridges, like giants turned to boulders by sunlight. Mab stared, mesmerized, as Harold continued to speak.

“You’re here to help break German codes, ladies, and the bombe machines have been designed by some of our cleverer chaps to help speed that process up. It’ll be tedious work keeping these beasts going, and precision is essential, so I’ve been authorized to share a bit more than usual about what they do.” He patted one of the massive cabinets like a dog. “Every cipher has a great many possible machine settings, and we can’t get any further on the decoding till we have the settings, and it’s slow going getting those by hand. These beasts will speed everything up, and that’s where you ladies come in. The brainy fellows will send over something like this.” Harold held up a complicated diagram of numbers and letters like nothing Mab had ever seen in Hut 6. “Called menus—”

“Why, sir?” one of the Wrens ventured.

“Probably because menu sounds better than worked-out guess.” Harold pushed his spectacles up. “You take the menu, plug up your machine accordingly—the plugs in the back correspond to the positions on the menu. Then start the machine up, and let her rip. Each wheel on the bombe”—he indicated the rows on the nearest machine—“goes through thousands of possible settings, faster than anyone could do by hand. It finds a possible match for the wheel wiring and ring setting, as well as one possible match for a plugboard letter. That leaves, oh, a few million million possible settings to check the other plugboard possibilities. When the machine finally stops, you’ll use the checking machine to match the stop position of the bombe, make sure you haven’t got a false positive, and so forth. Assuming you haven’t, you alert the boffins back in their huts that you’ve broken their setting for that key, then plug your machine up for the next menu and the next key. Questions?”

About a thousand, Mab thought. But that wasn’t how it was done here; at BP it was just button up the questions and have a go.

“Miss Churt and Wren Stevens, I’m putting you on this machine here. Someone named her Agnus Dei, or maybe just Agnus—”

Aggie, Mab thought, already disliking her. The machine’s back looked like a knitting basket crossed with a telephone switchboard—a mass of dangling plugs and great crimson pigtails of plaited wires like snarled yarn, snaking down through rows of letters and numbers. Wren Stevens looked similarly nonplussed. “I thought I’d ship out somewhere glamorous if I joined the navy,” she whispered to Mab as Harold began showing them how to keep the wires apart with tweezers. “Out to Malta or Ceylon, getting my drinks poured by lieutenants. Not buried in wiring in the middle of Buckinghamshire!”

“Good luck getting out now you’re in,” Mab said, still staring up at Aggie. “Nobody transfers out of BP unless you fall pregnant or go crazy, so take your pick.”

Servicing Aggie was like ministering to some cranky mechanical deity. Mab’s arms ached after an hour of hoisting heavy drums into their slots; her fingers were pinched red from the heavy clips that snapped each drum in place. Plugging up the back was a horror: wrestling with a mess of wires and coupling jacks, trying not to set sparks off, squinting at a menu that looked like an arcane diagramming exercise or maybe a spell for raising the dead. Mab jumped, fingertips buzzing, as a prickle of electricity shocked her for the fourth time, and set the machine going with a muttered curse. With all the bombes at full roar, the din of Hut 11 was incredible, pounding her ears like hammers.

“Work at the other drums while you wait for the machine to stop,” Harold shouted over the noise.

Mab pried open the drums to reveal circles of wire inside, going at the nest with tweezers to make sure not even a single one brushed against another and shorted the electrical circuit. Within the hour her eyes were smarting from the concentration and her reddened fingers pricked by copper wire. “What happens if the wires touch?” she called over the din.

“Don’t let the wires touch,” Harold replied simply.

Mab worked, sweat collecting between her aching shoulder blades, cuffs and wrists growing greasy from the bombe’s fine spray of oil droplets. Pushing limp, sweaty hair off her forehead, she straightened as Aggie stopped dead, every drum frozen. “Did we break it?” Mab asked as the other machines whirred.

“No, she’s telling you it’s time to check her results.” Harold showed Wren Stevens how to take the reading from the other side of the bombe, run it through the checking machine. “Agnus found the setting. Job’s up, strip her down, load the new drums, get the next menu going. Well done.”

He pushed another diagram into Mab’s hand. She knew it was for an army key because she’d seen the name on reports coming through her Hut 6 Typex, but everything else on the menu was a mystery. This was an earlier part of the BP information loop than she was used to seeing—the part that helped spit out those blocks of five-letter-grouped reports that landed on the desks of the Decoding Room women.

Mab couldn’t help a shiver. Working in the Decoding Room had a sheen of normality to it; a roomful of women hammering at Typex machines wasn’t so different from a roomful of secretaries in an office, chattering about wasn’t Gone with the Wind a swooner and have you seen the film yet? No one could chat in this din; no one would be admiring each other’s frocks when they were all dripping sweat in the windowless fug of machine oil. Mab had worked since she was fourteen, and she already knew there wasn’t a job in the world that could make this one seem normal. She finished plugging up Aggie and stood back. “Start her up.”

“BREAK TIME,” HAROLD called sometime later, tagging half the girls. “Relieve your partner in an hour.”

Mab didn’t want food, she wanted air. The Wrens headed for the NAAFI kiosk for tea, but Mab flopped on the lake’s grassy bank. Her ears rang dully from four hours of Aggie’s din; her fingers were pricked and stinging. She sucked down a cigarette and pulled her newest book out but gave up after five minutes. The Mad Hatters had picked a poetry collection for this month’s read—Mired, it was tersely and ominously called, a volume of Great War battlefield verses—and the rhythmic iambic pentameter beat in the same clackety-clack pattern as the bombe machine’s drums. “No, thank you,” she said aloud, tossing the book onto the grass.

“I don’t much like that book either,” a male voice remarked behind her.

Mab tilted her head back, looking up the rumpled suit to the broad face with its laugh lines. He looked vaguely familiar . . .

“It was very dark when we first met,” he said, smiling. “You changed my tire on a midnight road. Did the shoes fit?”

“Beautifully, thank you.” Mab smiled back, placing his face if not his name. “You really didn’t have to send them.”

“My pleasure.”

“Don’t suppose you could spare a cigarette?” Mab was down to her last one and had a feeling she’d need it badly at the end of shift. He produced a cigarette case. “I thought you didn’t work at BP.”

“No, London. Got sent over on a bit of business.”

Foreign Office? MI-5? Unnamed London fellows were always coming and going with their document cases and specially issued petrol coupons. Mab cast an appraising eye up at the chestnut-haired fellow, who gazed over the lake in silence. Good shoes, silver case for his cigarettes, rather lovely smile. What was his name? She didn’t want to admit she’d forgot altogether. “Don’t care for poetry?” she said, nodding at her discarded volume.

A shrug.

“Francis Gray isn’t terrible.” Educated London men liked girls who could talk about the use of metaphor and simile—you just had to be slightly less knowledgeable than they were. “‘The skyline, scarred with stars of rusted wire’—good lines, really, it’s just that the overall theme’s a bit obvious. I mean, equating a wartime trench to a sacrificial altar isn’t exactly original, is it?”

“Hackneyed,” he agreed. More silence.

“It’s this month’s pick for the Mad Hatters,” Mab tried again. “The BP literary society.” She got another of the lovely smiles, but no reply. Didn’t this one talk at all? She cut her losses, stubbing out her cigarette. “That’s the end of my tea break, I’m afraid.”

“Do you really dislike Gray’s poetry?” the chestnut-haired man asked. “Or are you pulling my leg?”

“I don’t dislike him. He’s just no Wilfred Owen. Not his fault—wasn’t he an absolute child when he wrote this?” One of those fellows who had lied about his age and enlisted far too young, Mab recalled vaguely, shoving her book into her handbag as she rose. “I didn’t know anything about poetry at seventeen.”

“Sixteen.”