And behind the notes in that one she found three small leaflets, each one of them made of two folded pieces of paper, a plain white sheet with a red cover. The cover was printed in German.

Jane turned the pages of one of the booklets with trembling hands. The inside of the cover was scrawled with neat, penciled text. The printed sheet in the middle was a grid of numbers and letters.

“Instructions and dial settings,” Jane whispered.

I hardly dared to breathe.

“The dials are called rotors. I was right: the key plate comes up and you can change them.” Jane studied Felix Baer’s written instructions. “Go on, try it!”

“I’ll break it!” I exclaimed.

“It’s quite robust. Let’s see how it works.”

It really was like having a wonderful new toy. Jane pored over Felix Baer’s penciled instructions and the printed charts, commenting aloud as she read, while I took the machine apart and fit it back together like a puzzle box. The mechanics of it were rather beautifully simple for such a complicated piece of machinery.

“These charts tell you the code settings for each day of the month for one group of the Luftwaffe,” Jane explained. “They change every day. He’s given us three months’ worth, but November is nearly finished. Phew! What a production military communications must be!”

We forgot everything else. We played with the German cipher machine until long after it got dark.

“All we need now is a message to decode,” I said wistfully.

The old woman laughed. “Better pack it up,” she said. “Then hide it all in the back of the wardrobe, under the furs.”

“But we ought to tell someone—!”

“We need the right person to tell, and the right way to tell them,” Jane said. Her pale blue eyes were excited in her wrinkled face. “Maybe the radio operator at the aerodrome? You needn’t say what you’ve found—just that you have information for the War Office. Ellen can arrange it, perhaps.”

I nodded. That made sense.

I placed the L key over the empty peg. Now it fitted perfectly.

I hid the incredible machine under Jane’s furs in the back of the wardrobe. Jane watched me open my flute case to put the cleaning rod back. She picked up her teacup, took a sip, and put it down again. It had gone stone cold hours ago.

“I would love to hear you play your flute, Louisa,” she said.

Tears stabbed at my eyes, and I squeezed them shut.

A man and a woman were crooning together on the radio, just as Mummy and Daddy used to do the minute he came into the house—even in England, where we had to use the piano in our landladies’ sitting room. First thing always when he got home from sea, they’d throw themselves down on the piano bench, and play and sing together.