Five rows in front of us I could see Maitland and Klaus talking intently, their heads close. But I wasn't ready to believe that a neurotic embassy attache with a feverish sense of adventure had mounted a one-man counter-espionage crusade against an organisation the size of Nemesis and persuaded a former Stasi colonel to put his trust in him.

I hadn't been able to do it myself, not completely, I knew that now.

'Aren't you running,' Helen said in a moment, 'a terrible risk?

'It depends on what you tell them.'

She turned her head quickly to look at me. 'I won't tell them anything, of course.'

'Then the risk I'm running isn't all that high.'

Not absolutely true. Klaus had got the whole thing worked out and I hadn't been able to stop him because I'd had to stick with my cover and go with him to Algeria, to Dar-el-Beida. It was possible that he believed in me, but it didn't make any difference one way or the other. We believe in what we want the truth to be, ignoring the evidence that would raise doubts, deceiving ourselves, and Dieter Klaus desperately wanted the truth to be that I was a bona fide arms dealer and could provide him with a Miniver NK-9 nuclear warhead. But he was a seasoned Stasi officer and he'd covered himself: if I made the rendezvous in Algiers and the NK-9 was delivered he'd be as happy as a kid at a Christmas tree – I am very pleased, you know, that you have offered me this particular item at such a convenient time – I am delighted! – but if there was no delivery he wouldn't be taking any risk: he'd still go ahead with his operation and he wouldn't let me walk away with all the information I had on him now. He would simply have me silenced.

'We're serving breakfast soon,' the stewardess said. Would you like to choose something from the menu? Leaning over us, the smile fixed, fright behind it, she wasn't with Nemesis, she was just flight crew that went with the Fokker, Marlene, the little brass tab on her uniform said, new to the job, hadn't any idea what her employer would be like, There are Eggs Benedict, if you care for them that way,' her heart still down there on the tarmac nursing a dog with a broken neck. 'And we'll be serving champagne in just a few minutes.' She took our order and moved on.

But the warhead would be there, and there on time: I wasn't worried about that. London would see to it.

He was quite adamant – we have to meet the deadline. Cone to Control. He would have got into Signals the moment we'd rung off last night.

You feel that if we don't make this delivery it's going to jeopardise the mission?

And the executive.

Cone would have said that. He had a sense of the humanities, could be counted on to let them know they'd have a dead ferret on their doorstep if they didn't get it right.

Very well, then. We shall do what is necessary.

There would have been a lot of phones ringing in the dead of last night, at the bedside of the head of the Army's Quartermaster Office and Ordnance Stores, if necessary of the Minister of Defence, if necessary of the Prime Minister, to whom the Bureau was directly responsible. Red tape would have been slashed through, security units alerted at the Ordnance hangars, passes shown and metal doors rolled back, the instructions presented and transport called in, the crew of a civilian freight-plane on Her Majesty's Service ordered to report for special duty, their destination sealed in an envelope to be opened in flight.

So Klaus would get his toy and I would be paid off if he kept to the deal – unless London made the decision to stake out the scene, and that was why I was sitting here with the feeling that time was running out for Solitaire and that it was only a matter of hours, because I knew London and I knew their way of thinking and their way of thinking was that if they could send in the SAS and Germany's GSG-9 and Algeria's counter-terrorist units they could do a better job of destroying Dieter Klaus and his whole organisation than one lonely ferret in the field, and unless I could reach a telephone in time and persuade them to change their thinking then that was what they'd do.

Finis, finito.

Looking down over the snows of the Swiss Alps I told Helen, 'I feel responsible for you. Did that occur?'

In surprise – 'No. Why should you?

'We brought you into Berlin to help us.'

'It doesn't matter.' Picking at her nails. 'I could have gone home yesterday morning if I'd wanted to. He – just rang me up, and asked me if I wanted to go to him. I – said I would.' She turned her head to look at me. 'I can't help it, you see.' With a note of bitterness – 'You wouldn't think, would you, that there could be so much passion under such a placid exterior?'

I offered the obvious cliche. 'Still waters.'

'Yes. Very still and very deep. Sometimes I frighten myself – but anyway, you don't have to feel responsible for me any more. I'm a free agent.'

'Are you?

Her smile was quick, nervous. 'All right, I'm free to trap myself in this – in this thing that's going on.'

'Do you know what it is?

She didn't look away. 'No, I don't. Do you believe me?

'Of course.'

'They haven't told me anything,' she said, 'and I haven't asked. None of these people here know what Dieter's planning to do, except for George.' A moment of hesitation, then: 'I think he sort of switched sides.'

'George?'

'Yes. I haven't talked to him very much since I went back to him, because Dieter's had meetings all the time and George has been kept busy; but obviously I had to ask him what all that drama was about, the murder scene at his flat, and he said Dieter had – I must get it right – had "required it of him". He wouldn't say any more.'

Perhaps it had been a blooding, then, a ritual act of faith, of commitment. George had become excited by Nemesis and had wanted to go over -'switch sides' from counter-terrorism to terrorism -and Klaus had demanded that he go through a symbolic act of self-immolation as his entree into the organisation. It could have appealed to Maitland's neurotic fancies: he could even have revelled in the idea of such grand deception. But he must also have brought something to Nemesis, something of value – as I had. He was already close to Dieter Klaus, on equal terms.

I asked Helen, Why did Klaus accept him, do you think?

'I don't know. He might have made some kind of proposal. He was always playing around with outlandish schemes in his mind.'

Like assassinating Gadhafi, for instance. Possible scenario, then: Klaus had been planning a terrorist operation and Maitland had gone to him and said look, do it this way, it's better. Or bigger. So Klaus had taken him up on it and there wasn't going to be another Lockerbie, there was going to be something bigger than that, even more devastating. The purpose, after all, of any terrorist act was to attract attention.

The snows drew out beneath us, twenty thousand feet below. I thought I could make out the Matter-horn.

'These meetings,' I said. 'You weren't invited to any?'

'Oh, no. I'm just… here to be with George. But I heard him talking to someone on the phone about "Mittenaeht Ein" and "Mittenacht Zwei", and I heard Dieter using the same phrases. My German's not good at all but they stuck in my mind: they were repeated so often.'

They were obviously code names and possibly for deadlines and if one of them were for midnight tonight it'd be only five hours after delivery of the Miniver and they'd be running it very close.

She must have heard other things, a word here and there, things she'd half-forgotten because they hadn't sounded important, though I might see them as vital. I could coax her memory, as I'd done with Willi Hartman, and conceivably bring out information I could use; but it would be too dangerous for her. If anything she'd given me became the basis of my future actions and Klaus suspected the source…