Jane and I had left Felix Baer’s leaflets lying beneath the lid on top of the keyboard. I opened the first booklet. I couldn’t read the German headings, but Jane had explained to me how to match up the rotors and plugs. The two groups of three letters on Bill Yorke’s cigarette paper told me where the message began. I knew from Felix Baer’s instructions that when I keyed them in with today’s settings, they’d give me the starting letters for the rotor dials. I took a deep breath and began to type. I didn’t really believe it would work.

I couldn’t decode it quickly. There weren’t any proper words to look at or remember. I had to do it letter by letter, and pay attention to make sure I was hitting the right keys. I hadn’t thought to bring extra paper, so as the decoded letters lit up in the upper keyboard, I wrote them down on the blank endpaper at the back of my book.

After five minutes of struggle and with my back starting to ache from leaning down to the floor to hit the keyboard, I sat up and read in my notebook what the lamplit letters had spelled out:

FEIND LICHE NSCHL ACHTS CHIFF E…

It didn’t look like nonsense.

I tried rewriting it by putting spaces between some of those bunches of consonants, and got:

FEIND LICHENS CHLACHTS CHIFFE…

And that looked like German.

The hair stood up at the back of my neck.

I couldn’t read this, but I could tell it was real words. Maybe I hadn’t split them the right way. But those letters meant something.

And with the cipher machine, I’d worked it out myself.

For a moment I was so excited I thought I was going to be sick.

I thumped my fist on the floor. Then I regretted that in case anyone heard it. I was all cooped up in this tiny little room and I wanted to shout and jump up and down, but there wasn’t room to do anything, and also I knew this was as secret as secret could be, and whatever I did, I mustn’t shout.

I had to tell Jamie Beaufort-Stuart. I had to figure out the whole message, and then the next time his squadron of Blenheim bombers went flying out over the North Sea, they’d know ahead of time what they were going to run into.

So the only thing to do was to sit there and decode the rest of it.

I was about to explode with excitement when I finally went back to Room Number Five. I felt as if I were tumbling to earth in a bomb dropped from a plane, Luftwaffe or RAF, I couldn’t quite work out which.