She heaved a sigh and let her eyes slide shut. Let the intercepted telegram that had come zipping up the pneumatic tubes just after midnight play before her eyelids. Let the numbers she assigned to correspond to each word go from marching to jumping.

“That’s what we said last time. I’ll not go out hanging my head again. Dilly didn’t stop mocking me about it all week. I—”

“Got it!” Margot surged forward as those beautiful digits settled at last into her mind in the proper order. Ignoring the rustling of her colleagues as they slid over to look at her work, she picked up her pen again and scratched the final numbers into the column on her paper. Checked it against the telegram. Breathed a laugh as she finally was able to scrawl the decrypt of the intercepted message onto the fresh sheet of paper.

“Ah.” De Grey gave her shoulder a friendly whack. “Good man.”

Were Maman in her usual spot at the desk by the door, her lips would have thinned at that compliment—as they always did every time the other cryptographers seemed to forget she was a young woman and not another of them. But Margot grinned. And took a moment to be grateful that the secretaries weren’t obliged to take a night shift once a week like the cryptographers were.

Victory sang through her veins. Three, nine, twenty-seven, eighty-one, two forty-three . . .

“You have saved us infinite shame, De Wilde.” Culbreth nodded, almost smiling, and then wilted onto his desk. “Have we time for a nap, do you think?”

“Doesn’t sound like it.” Margot could just make out the first of the morning’s footfalls on the stairs and the ding of the lift. The Old Building, or OB as they often called it, was coming to life.

She took a moment to order her desk while her colleagues did the same. To obliterate, as much as possible, the evidence of a night hard at work—empty cups, the stale crust of what had been a sandwich, eraser leavings. They had no cleaning ladies in the hive of Room 40. No girls to wheel in tea carts and wheel out the dishes. What tidying got done, they did themselves. The decrypt she’d just managed in hand, she stood and turned to her mother’s desk. Her eyes skimmed the message again. It was a list of ships, possible targets for the U-boats that day. Boynton. City Of Swansea. Dinorah.

Nothing out of the ordinary. She’d long ago given up wishing they could send a warning to each one. They couldn’t—it would mean revealing to Germany that they intercepted their every message. It would compromise Room 40. It was a form of yosu-miru, as the terms of the game Go stated it—a move that might require sacrifice, but for a greater purpose.