Hall grunted. “You’re right. Our minelaying code must have been compromised—that’s the only way they’d know when our sweepers would be out clearing the waters. Well.” A mischievous twinkle entered his eyes—the very sort that had always been in Papa’s whenever he had an idea for a new puzzle to hide for her. “If they have our minelaying code, let’s use it against them. Would you mind encrypting something for me too?”

In answer, she pulled out a blank sheet of paper and handed him her pen. If it was something to be put into the minelaying code, which she suspected it was, she’d have to fetch the codebook from downstairs. But for the pleasure of getting to encrypt and not just decrypt, it would be well worth the exercise.

Hall leaned over and scratched a message onto the page. In minelaying code. Harbor clear. He drew a horizontal line under that quick message and then wrote In personal code. To harbor master. Close harbor to all traffic. Do not—I repeat, do not—clear mines already laid.

The light of mischief traveled from his eyes to the corner of his mouth, which turned up in a smile. “There we are. We’ll send the all clear tomorrow, which the huns will intercept, letting them think all their mines are gone. Then, when they come to lay more, they’ll come across the ones still there. How is that for turnabout?”

Margot chuckled and accepted the pen back from him. “Perfect, DID.”

He patted her shoulder again and then turned away. “Just leave the encrypted telegram with the decrypt of the other on my desk, if you would. Thank you, Margot.”

“Of course.” She picked up her pen again and went back to the original U-boat message. It only took her a few minutes to work through the rest of it, given that she’d almost been finished already. There. She set the completed decrypt into the basket for a secretary to type up and deliver to Commander James. And then she turned to the work from Hall.

First, the fun bit. She rarely had the opportunity to encode anything, so she took the five minutes necessary to fetch the British minelaying codebook from downstairs, then pulled out Hall’s personal code from her own desk drawer and got down to the pleasurable task of encrypting. Given the brevity of the messages, it didn’t take long.

But it made the numbers hum in her mind. It made her shoulder warm where Hall had patted it—where Papa always had too, when she’d managed a task he’d thought would challenge her. Where sometimes she imagined God resting His hand.

She turned then to the message from Thoroton. With Hall’s codebook still before her, she got down to work on the considerably longer message from their head of intelligence in the Med.