Enigma

down on his unmade bed, still wearing his coat and scarf. Presently he heard footsteps and someone knocked.
    'Breakfast, sir.'
    'Just leave it outside. Thank you.'
    'Are you all right, sir?'
    'I'm fine.'
    He heard the clatter of the tray being set down, and steps retreating. The room seemed to be lurching and swelling out of all proportion, a corner of the ceiling was suddenly huge and close enough to touch. He closed his eyes and the visions came up at him through the darkness -
    —Turing, smiling his shy half smile: 'Tom, I can assure you, I am making no progress on Riemann whatsoever . . .'
    —Logie, pumping his hand in the Bombe Hut, shouting above the noise of the machinery, 'The Prime Minister has just been on the telephone with his congratulations ..."
    —Claire, touching his cheek, whispering, 'Poor you, I've really got under your skin, haven't I, poor you . . .'
    —'Stand back'—a man's voice, Logie's voice—'Stand back, give him air . . .'
    And then there was nothing.
    When he woke, the first thing he did was look at his watch. He'd been unconscious for about an hour. He sat up and patted his overcoat pockets. Somewhere he had a notebook in which he recorded the duration of each attack, and the symptoms. It was a distressingly long list. He found instead the three envelopes.
    He laid them out on the bed and considered them for a while. Then he opened two of them. One was a card from his mother, the other from his aunt, both wishing a happy birthday. Neither woman had any idea what he was doing and both, he knew, were guiltily disappointed he wasn't in uniform and being shot at, like the sons of most of their friends.
    'But what do I tell people?' his mother had asked him in despair during one of his brief visits home, after he had refused yet again to tell her what he did.
    'Tell them I'm in government communications,' he had replied, using the formula they had been instructed to deploy in the face of persistent enquiries.
    'But perhaps they'd like to know a little more than that.'
    'Then they're acting suspiciously and you should call the police.'
    His mother had contemplated the social catastrophe of her bridge four being interviewed by the local inspector, and had fallen silent.
    And the third letter? Like Kite before him, he turned it over and sniffed it. Was it his imagination or was there a trace of scent? Ashes of Roses by Bourjois, a minuscule bottle of which had practically bankrupted him just a month earlier. He used his slide rule as a paperknife and slit the envelope open. Inside was a cheap card, carelessly chosen—it showed a bowl of fruit, of all things—and a standard message for the circumstances, or so he guessed, never having been in this situation before. 'Dearest T . . . always see you as a friend . . . perhaps in the future . . . sorry to hear about ... in haste . . . much love . . .' He closed his eyes.
    Later, after he had filled in the crossword, after Mrs Sax had finished the cleaning, after Bickerdyke had deposited another tray of food and taken it away again untouched, Jericho got down on his hands and knees and tugged a suitcase from beneath his bed and unlocked it. Folded into the middle of his 1930 Doubleday first edition of The Complete Sherlock Holmes were six sheets of foolscap covered in his tiny writing. He took them over to the rickety desk beside the window and smoothed them out.
    'The cipher machine converts the input(plain language, P) into the cipher (Z) by means of a function f. Thus Z=f(P,K) where K denotes the key..."
    He sharpened his pencil, blew away the shavings and bent over the sheets.
    'Suppose K has N possible values. For each of the N assumptions we must see if f(Z,K) produces plain language, where f'1 is the deciphering function which produces P if K is correct
    The wind ruffled the surface of the Cam. A flotilla of ducks rode the waves, without moving, like ships at anchor. He put down his pencil and read her card again, trying to measure the emotion, the meaning behind the flat phrases. Could one, he wondered, construct a similar formula for letters—for love letters or for letters signalling the end of love?
    'The input (sentiment, S) is converted into a message (M) by the woman, by means of the Junction w. Thus M=w(S,V) where V denotes the vocabulary. Suppose V has N possible values ...'
    The mathematical symbols blurred before his eyes. He took the card into the bedroom, to the grate, knelt and struck a match. The paper flared briefly and