'I got it from my typewriter,' Jane said.' Or that started me off. I use a Canon AP810-III, and I was changing the ribbon when I noticed the characters on the old one. It's a wide ribbon and they're not in a single-line row, it prints three characters vertically, shifts — wait a minute — ' she reached for her pad and got a pencil — ' it prints three characters vertically downwards, then shifts one space to the right and prints upwards again, three — ' she glanced up at me — ' am I being an infant prodigy all over you?'

'I've worked on codes,' I said. 'I'm interested.'

'All right. Three down, then shift, three up, shift, three down again, like this. And if you read it like that, it makes sense, but we always read in a single line from left to right, and that looked like gibberish, and it suddenly struck me — I was looking at a code.' she put the pencil down and bit on some toast and munched it. 'But if we, say, typed the words, oh, I dunno, "if you like", the «y» comes at the bottom of the first vertical and the «o» comes at the bottom of the next one, and there aren't too many ordinary words beginning with «yo» except for «you» — and you start getting the drift. So at the top and bottom of every vertical I inserted a blind character to break the rhythm, and that was much nicer.' she sat back and looked at me. 'Had enough?'

'No.'

' Glutton for punishment. So I 'm reading three horizontal lines of code and I'm not picking up clues from the verticals because of the blinds. At that stage it would have taken a bright teenager maybe half an hour to break, so I threw in a reverse-direction read-out and put it on the standard grid and went for three-character alphabetical substitutes and froze it. Mystere!' she shook her pony-tail. 'God, don't tell the man in London.' Her eyes were suddenly deep, their colour darkening. 'Or anyone.'