‘So I believe that the key to RECOVERY must be hidden in the message. But where is it hidden? If it were just like ULTRA, and on even-number days it was this set of numbers and on odd-number days it was that set, neither Sivincy herself nor the American army that was employing her would have been happy with it. Within the limitations imposed by her cipher, she would certainly want to work out an unusual and clever new key. After I considered that for a bit, I remembered that Sivincy at an earlier stage in her career discovered a mathematical principle which is called the Shadow Principle or the Light Principle, popularly known as Honeycomb Theory. The substance of this theory is that if you take any given honeycomb structure, with the help of a moving light source, you can distinguish black and white, shadow and light. Right now I don’t have the equipment, so I can’t demonstrate it for you.’

‘I can imagine it. For example, if the roof was in fact made of some honeycombed substance, we’d see pinpricks of light.’

‘Exactly. And what’s the point of all this? It means that if you make sure you are forever moving at the same speed as the light, you can always keep yourself hidden in the shadows. This has significant implications for astrophysics.’

I felt she was wandering away from the point. ‘Let’s get back to our key.’

‘Right now I’m making my cryptographic bombe. When it’s finished we’ll give it a run-through, and then you’ll understand.’

I opened my eyes wide. ‘So all that banging about in your room, and those things like bottles and bowling balls was all preparation for a cryptographic bombe?’

‘Yes. What did you think I was doing?’

I was embarrassed. ‘Chen thought you were playing some stupid game.’

She sniffed. ‘You people really do look at everyone else in such a negative way!’

I quickly apologized for misunderstanding her, but I wasn’t expecting her to giggle and say charmingly that as long as I understood that she loved me, she didn’t care about anything else. As she spoke, she reached for my hand. Fortunately I had already made my request that she should obey me, otherwise she would have caused even more trouble on this occasion.