'May I see what he was carrying?' I asked.

'He had that small shoulder-bag containing shaving things and some underwear, a newspaper and aspirins and so on. That's over there. I found nothing of interest in it. But he was also carrying this.' Nicol pointed to a hard brown leather case on the side-table. It was an expensive piece of luggage without any manufacturer's labels, a one-suiter with separate spaces for shoes, shirts and socks. I suppose the factory made it to the maximum regulation size for cabin baggage, but it was large enough to get anyone into a lot of arguments with officious check-in clerks.

One compartment inside the lid was intended for business papers. It even had special places for pens, pencils and a notebook. Inside the zippered section there were four lots of typed pages, each neatly bound into varying-coloured plastic folders. I flipped through the pages quickly. It was all in English, but it was unmistakably American in presentation and content. The way in which these reports had been prepared – with coloured charts and captioned photos – made them look like the sort of elaborate pitch that an advertising agency might make to a potential client.

The introduction said, 'The German yard Howaldtswerke Deutsche Werft at Kiel has dominated the market in small- and medium-size diesel submarines for more than 15 years. Two Type 209 (1400t.) submarines are being fitted out and Brazil has ordered two of the same displacement. Work on these will start almost immediately. Two larger (1500t.) boats are already begun for delivery to India. These will not be stretched versions of the Type 209 but specially designed to a new specification.'

Soon, however, the detailed descriptions became more technical: 'The Type 2095 carry Krupp Atlas passive/active sonar in the sail but the TR 1700 also have a passive-ranging sonar of French design. The fire-control system made by Hollandse Signaal-Apparaten is standard, but modifications are being incorporated following the repeated failure of the Argentine submarine San Luis in attacks against the Royal Navy task force.'

'It doesn't look like you've captured a master spy,' I said.

'It's marked secret,' said Nicol defensively.

'But so are a lot things in the museum archives,' I said.

'Never mind the archives, this is dated last month. I don't know anything about submarines, but I know the Russians give a high priority to updating their knowledge of the world's submarines. And I know that these diesel ones are the hunter-killers that would have to be used to find their nuclear-powered ones.'

'You've been watching too many TV documentaries,' I said.

'And I've learned enough at NATO security conferences to know that a report like this that reveals secrets about submarines built in German yards for the Norwegian and Danish navies will get everyone steamed up.'

'There's no denying that,' I said. 'We think Biedermann is a smalltime KGB agent working out of Berlin. Where was he going?'

'I can't tell you.'

'Can't tell me, or don't know?' I said.

'He arrived from Paris in a taxi cab and hadn't yet bought a ticket. Look for yourself.' Nicol indicated Biedermann's personal possessions which were still on the desk.

'So it was a tip-off?'

'A good guess,' said Nicol.

'Don't give me that, Gérard,' I said. 'You say he hadn't bought a ticket. And he hadn't arrived by plane. So he wasn't going through Customs, immigration or a security check when you found the papers. Who tipped you off to search him?'

'Tipped off?'

'The only reason you know all that printed junk is secret is because you were tipped off.'

'I hate policemen, don't you, Bernard? They always have such nasty suspicious minds. I never mix with them off-duty.'

'American passport. Have you told the embassy?'

'Not yet,' he said. 'Where is Biedermann resident?'

'Mexico. He has companies registered there. For tax purposes, I suppose. Is he talking?'

'He helped us a little with some preliminary questions,' admitted Nicol.

'A passage à tabac? I said. It was delicate police euphemism for the preliminary roughing up that was given to uncooperative prisoners under interrogation.

He looked at me blank-faced and said, That sort of thing doesn't happen any more. That all stopped fifty years ago.'

'I was only kidding,' I said, although I could have opened my shirt and showed him a few scars that proved otherwise. 'What's the official policy? Are you holding on to the prisoner, or do you want me to take him away?'

'I'm waiting for instructions on that,' said Nicol. 'But it's been agreed that you talk to him.'

'Alone?'

Nicol gave me a mirthless grin. 'Providing you don't get rough with him and try and blame it on to our primitive police methods.'

So my taunt did find its mark. Thanks,' I said. 'I'll do the same for you some time.'

'It was a tip-off. It was phoned through to my office, so it was someone who knew how the Sûreté works. The caller said a man would be at the Alitalia desk; a scarred face, walks with a limp. A clerk took the call. There's no chance of identifying the voice or tracing the call but you can talk to the clerk if you wish. A man; perfect French, probably a Paris accent.'

'Thanks,' I said. 'Sounds like you've already narrowed it down to eight million suspects.'

'I'll get someone to take you downstairs.'

They were holding Paul Biedermann in the specially built cell block that is one floor below the police accommodation. It is a brickbuilt area with a metal-reinforced ceiling. In 1973 – by which time airports had become a major attraction for hijackers, assassins, demonstrators and lunatics and criminals of every kind – the cell block was tripled in size and redesigned to provide twenty-five very small solitary cells, eight cells with accommodation for three prisoners each (current penology advising that four prisoners together fight, and two get too friendly), and four rooms for interrogating prisoners in secure conditions. Three cells for women prisoners were also built at that time.

Paul Biedermann was not in a cell of any sort. They were holding him in one of the interrogation rooms. Like most such rooms it had a small observation chamber large enough for two or three people. The door to that was unlocked and I stepped inside it and watched Paul Biedermann through the mirrored glass panel. There was all the usual recording equipment here but no sign of its being recently used.

The interrogation room in which Biedermann was being held had no bed; just a table and two chairs. Nothing to be broken, bent or used as a weapon. The door was not a cell door; there was no iron grill or bolts, and it was secured only by a heavy-duty mortise lock. After I'd had a good look at him I opened the locked door and went inside.

'Bernd. Am I glad to see you.' He laughed. The scars down the side of his face puckered, and his smile was so broad that his twisted face looked almost demented. 'Jesus. I was hoping it would be you. They said that someone was coming from Berlin. I can explain everything, Bernd. It's all a crazy mistake.' Even under stress he still had that low-pitched hoarse voice and the strong American accent.

'Easy does it, Paul,' I said. I looked around the white-tiled room but I couldn't see any obvious signs of hidden microphones. If the observation chamber was not in use they were probably not recording us. Finally I decided not to worry too much about it.

'I did everything you told me to do, Bernd. Everything.' He was wearing expensive linen pants and open-neck brown shirt with a scarf tied at the neck. There was a soft brown cashmere jacket thrown carelessly on to one of the chairs. 'Have you got a cigarette? They even took away my cigarettes. How do you like that.'