Enigma

older than himself, as shy as a freshman, with a hank of dark hair falling across his eyes: the great Alan Turing, the author of On Computable Numbers, the progenitor of the Universal Computing Machine . . .
    Turing had asked him what he proposed to take as his subject for his first year's research.
    'Riemann's theory of prime numbers.'
    'But I am researching Riemann myself.'
    'I know,' Jericho had blurted out, 'that's why I chose it.'
    And Turing had laughed at this outrageous display of hero worship, and had agreed to supervise Jericho's research, even though he hated teaching.
    Now Jericho stood on the landing and tried Turing's door. Locked, of course. The dust smeared his hand. He tried to remember how the room had looked. Squalor had been the overwhelming impression. Books, notes, letters, dirty clothes, empty bottles and tins of food had been strewn across the floor. There had been a teddy bear called Porgy on the mantelpiece above the gas fire, and a battered violin leaning in the corner, which Turing had picked up in a junk shop.
    Turing had been too shy a man to get to know well. In any case, from the Christmas of 1938 he was hardly ever to be seen. He would cancel supervisions at the last minute saying he had to be in London. Or Jericho would climb these stairs and knock and there would be no reply, even though Jericho could sense he was behind the door. When, at last, around Easter 1939, not long after the Nazis had marched into Prague, the two men had finally met, Jericho had nerved himself to say: 'Look, sir, if you don't want to supervise me . . .'
    'It's not that.'
    'Or if you're making progress on the Riemann Hypothesis and you don't want to share it..."
    Turing had smiled. 'Tom, I can assure you I am making no progress on Riemann whatsoever.'
    Then what. . . ?'
    'It's not Riemann.' And then he had added, very quietly: 'There are other things now happening in the world, you know, apart from mathematics . . .'
    Two days later Jericho had found a note in his pigeonhole.
    'Please join me for a glass of sherry in my rooms this evening. F.J. Atwood.'
    Jericho turned from Turing's room. He felt faint. He gripped the worn handrail, taking each step carefully, like an old man.
    Atwood. Nobody refused an invitation from Atwood, professor of ancient history, dean of the college before Jericho was even born, a man with a spider's web of connections in Whitehall. It was tantamount to a summons from God.
    'Speak any languages?' had been Atwood's opening question as he poured the drinks. He was in his fifties, a bachelor, married to the college. His books were arranged prominently on the shelf behind him. The Greek and Macedonian Art of War. Caesar as Man of Letters. Thucydides and His History.
    'Only German.' Jericho had learned it in adolescence to read the great nineteenth-century mathematicians—Gauss, Kummer, Hilbert.
    Atwood had nodded and handed over a tiny measure of very dry sherry in a crystal glass. He followed Jericho's gaze to the books. 'Do you know Herodotus, by any chance? Do you know the story of Histiaeus?'
    It was a rhetorical question; Atwood's questions mostly were.
    'Histiaeus wished to send a message from the Persian court to his son-in-law, the tyrant Aristagoras, at Miletus, urging him to rise in revolt. However, he feared any such communication would he intercepted. His solution was to shave the head of his most trusted slave, tattoo the message onto his naked scalp, wait for his hair to grow, then send him to Aristagoras with a request that he be given a haircut. Unreliable but, in his case, effective. Your health.'
    Jericho learned later that Atwood told the same stories to all his recruits. Histiaeus and his bald slave gave way to Polybius and his cipher square, then came Caesar's letter to Cicero using an alphabet in which a was enciphered as d, b as e, c as f, and so forth. Finally, still circling the subject, but closer now, had come the lesson in etymology.
    'The Latin crypta, from the Greek root kpvTTpt? meaning “hidden, concealed”. Hence crypt, burial place of the dead, and crypto, secret. Crypto-communist, crypto-fascist ... By the way, you're not either, are you?'
    'I'm not a burial place of the dead, no.'
    ' Cryptogram.. .' Atwood had raised his sherry to the light and squinted at the pale liquid. 'Cryptanalysis. . .Turing tells me he thinks you might be rather good . . .'
    Jericho was running a fever by the time he reached his rooms. He locked the door and flopped face