Enigma

replies.' He riffled through the log sheets. 'Easy contact on the 9th as well, and again on the 20th. Ah,' he said, 'now on the 2nd of March it looks to have been more tricky.' The form was indeed a mass of terse dialogue. He held it up to the light. Smolensk to Berlin: QZE, QRJ, QRO. (Your frequency is too high, your signals are too weak, increase your power.) And Berlin snapping back: QWP, QRXIO (observe regulations, wait ten minutes) and finally an exasperated QRX (shut up). 'Now this is interesting. No wonder they suddenly start to sound like strangers.' Jericho squinted at the carbon copy. 'The call sign in Berlin has changed.'
    'Changed? Absurd. Changed to what?'
    'TGD.'
    'What?. Let me see that.' She snatched the form out of his hand. 'That's not possible. No, no. TGD simply isn't a Wehrmacht call sign.'
    'How can you be sure?'
    'Because I know it. There's a whole Enigma key named after TGD. It's never been broken. It's famous.' She had started to wind a lock of hair nervously around her right index finger. 'Notorious might be a better word.'
    'What is it?'
    'It's the call sign of Gestapo headquarters in Berlin.'
    'Gestapo?' Jericho fumbled through the remaining log sheets. 'But all the messages from March the 2nd onwards,' he said, 'that's eight out of the eleven, all the long ones, including the four in Claire's room—they're all addressed to that sign.' He gave the forms to her so she could check for herself and sat back in his seat.
    A gust of wind stirred the branches above them, sending a shower of rainwater rattling like a volley across the windscreen.
    'Let's try and construct a thesis,' said Jericho after a minute or two, as much to hear a human voice as anything. The random pattering of the downpour and the crepuscular gloom of the forest were beginning to affect his nerves. Hester had pulled her feet up from the sodden floor and was huddled up very small on the front seat, staring out at the forest, hugging her legs, occasionally massaging her toes through her damp stockings.
    'March the 4th is the key day,' he went on. (Where was I on 4 March? In another world: reading Sherlock Holmes in front of a Cambridge gas fire, avoiding Mr Kite and learning to walk again) 'Up to that day, everything is proceeding normally. A signals unit hibernating in the Ukraine, dormant all winter, has come to life in the warmer weather. First, a few signals to Army HQ in Berlin, and then a burst of longer traffic to the Gestapo -'
    'That's not normal,' said Hester scathingly. 'An Army unit transmitting reports in a Russian-front Enigma key to the headquarters of the secret police? Normal? I'd call that unprecedented.'
    'Quite.' He didn't mind being interrupted. He was glad of a sign she was listening. 'In fact, it's so unprecedented, someone at Bletchley wakes up to what's happening and starts to panic. All previous signals are removed from the Registry. And just before
    midnight on that same day your Mr Mermagen telephones Beaumanor and tells them to stop interception. Ever happen before?'
    'Never.' She paused, then moved her shoulder slightly in concession. 'Well, all right, maybe, when traffic's very heavy, a low-priority target might be neglected for a day or so. But you saw the size of Beaumanor. And that's not as big as the RAF's station at Chicksands. And there must be a dozen smaller places, maybe more. We're always being told by people like you that the whole point of the exercise is to monitor everything?
    He nodded. This was true. It had been their philosophy from the beginning: be inclusive, miss nothing. It isn't the big boys who give you the cribs—they're too good. It's the little fellows—the long-forgotten incompetents stuck in out-of-the-way places, who always begin their messages 'situation normal, nothing to report' and then use the same nulls in the same places, or who habitually encipher their own call-signs, or who set the rotors every morning with their girlfriend's initials . . .
    Jericho said: 'So he wouldn't have told them to stop on his own authority?'
    'Miles? God, no.'
    'Who gives him his orders?'
    'That depends. Hut 6 Machine Room, usually. Sometimes the Hut 3 Watch. They decide priorities.'
    'Could he have made a mistake?'
    'In what sense?'
    'Well, Heaviside said Miles called Beaumanor just before midnight on the 4th in a panic. I was wondering: what if Miles had been told earlier in the day that this unit was no longer to be intercepted, but forgot to pass on the message.'
    'Eminently