'The only thing we'll learn from it', I added, 'is that the KGB chose a document that will involve the maximum number of security organizations: France, Denmark, Norway, Britain, several Latin American customers. Mexico where he was resident and the US because of his passport.'

'But the material was important enough for him to be killed,' said Tiptree.

'He was killed to incriminate me,' I said.

'Well,' said Tiptree with studied patience. There's no avoiding the fact that you gave him the drink that poisoned him.'

'But I didn't know what it was. We've been through all that. Just before we came in here Bret told me that the Sûreté have even found someone who identified the girl who gave me the poisoned coffee.'

Bret fidgeted in his chair. He liked to swing round in his swivel chair in his office. This wasn't a swivel chair but Bret kept throwing his weight from one side to the other as if hoping that it might become one. He corrected me. 'I said, the Sûreté found someone in the building who remembered seeing the girl you described. Hardly the same thing, Bernard. Hardly the same thing.'

'You say that Biedermann was of no account,' said Tiptree, still exhibiting that mannered patience with which great minds untangle ignorance. 'I wish you could give us just one reason for believing that.'

'Biedermann was so unimportant that the KGB killed him just to implicate me. Doesn't that prove something?'

Bret said, 'It proves nothing, as well you know. For all we can figure, Biedermann was in this up to his neck and you were working with him. That sounds a more likely motive for his murder. That explanation shows why you made him sacred without putting his name on our copy of the filing sheets.'

'I wanted a favour from him. I was preparing the way for it.'

'What favour?'

'I wanted him to help me persuade Stinnes.'

Bret said, 'What help were you going to get from the unimportant little jerk you described?'

'Stinnes was in contact with Biedermann. I thought Stinnes would choose to work through him instead of Werner Volkmann.'

'Why?'

'It's what I would have done.'

'So why didn't Stinnes do it through Biedermann?'

'I think he planned to do it that way but that the KGB began to get worried about what was happening and stopped him.'

'Play that back at half-speed,' said Bret.

'I think Moscow encouraged Stinnes to tease us a little at first. But then Stinnes realized he had the perfect cover for coming over to us. But Moscow never trusts anyone, so I think they are monitoring Stinnes and his contacts with us. He has an assistant – Pavel Moskvin – who might be someone assigned by Moscow Centre to spy on him. It could well be that they have other people spying on him. We all know that Moscow likes to have spies who spy on spies who spy on spies. I think someone higher up told Stinnes not to use Biedermann as the go-between. They had other plans for Biedermann. He was to be murdered.'

Bret fixed me with his eyes. We both knew that by 'someone higher up' I meant Fiona. I half expected him to say so. Once I'd suspected him of being Fiona's lover. Even now I'd not entirely dismissed the idea. I wonder if he knew that. He said, 'So you thought Biedermann would be valuable to us. That's why you made him sacred?'

'Yes,' I said.

'Wouldn't it be simpler, and more logical, to think you covered for Biedermann because he was a buddy?'

'Are we looking for simplicity and logic?' I said. 'This is the KGB we're talking about. Let's just stick to what is likely.'

'Then how likely is this?' said Bret. 'Biedermann is your KGB contact. You make him sacred to keep everyone else off his back. That way you'll be the first to hear if he attracts the attention of any NATO intelligence agency. And your excuse for contacting him, any time you want, night or day, is that you are continuing the investigation into his activities.'

'I didn't like Biedermann. I've never liked him. Anyone will tell you that.' It was a feeble response to Bret's convincing pattern and he ignored it.

'That sort of cover – investigation – has been used before.'

'Biedermann was killed in order to frame me for his murder, and because while he was alive his evidence would support everything I've told you. There's no other reason for what was otherwise a completely gratuitous killing.'

'Oh, sure,' said Bret. 'All to get you into deep trouble.'

I didn't answer. The KGB's operational staff had done their work well. Given all the facts against some other employee of the department, I too would have been as suspicious as Bret was.

Dicky stopped biting his nail. 'Shall I tell you what I think,' said Dicky. His voice was high and nervous but it wasn't a question; Dicky was determined to share his theory. 'I think Stinnes never gave a damn about Biedermann. That night in Mexico, when he first made contact with the Volkmanns, he apparently went across to the table because he mistook Zena Volkmann for the Biedermann girl, I say Stinnes was after Zena Volkmann. Hell, she's a stunner, you know, and Stinnes has a reputation as a woman chaser. I think we're making too much of Biedermann's role in all this.'

'Well, think about this one,' I said. 'Suppose Stinnes was sent to Mexico City only because Zena and Werner were already there. He told them that he'd been there a few weeks but we have no proof of that. We've been congratulating ourselves on the way that we put out an alert and then the Volkmanns spotted him. But suppose it's the other way round? Suppose Stinnes knew exactly who the Volkmanns were that night when he went over to their table in the Kronprinz Club? Suppose the whole scenario had been planned that way by the KGB operational staff.'

I looked around. 'Go on,' said Bret. 'We're all listening.'

I said, 'How could he mistake Zena Volkmann for Poppy Biedermann? No one could mistake one for the other; there's no resemblance. He pretended to mistake Zena for the Biedermann girl in order to bring Biedermann into the conversation, knowing that we'd find out Paul Biedermann was in Mexico and that we'd make contact with him. Suppose they were thinking of involving Biedermann right back when we started?'

'With what motive?' said Dicky and then regretted saying it. Dicky liked to nod things through as if he knew everything. He touched his bloodless lips as if making sure his mouth was shut.

'Well, he's not done too badly, has he?' I said. 'He's got everyone here jumping up and down with excitement. You're accusing me of being a KGB agent and of murdering Biedermann on KGB instructions. Not bad. We'd be very proud to have the KGB floundering about like this, trying to find out who's on which side.'

Bret frowned; my accusation of floundering found a target. Frank Harrington leaned forward and said, 'So how far will they go? Send Stinnes here to give us a lot of misinformation?'

'I doubt if he could sustain a prolonged interrogation.'

'Then why the hell would they bother?' said Bret.

'To get me to run, Bret,' I said.

'Run to Moscow?'

'It fits. They send Stinnes to Mexico so that Volkmann will spot him because they guess that I'll be the chosen contact. And then they plan Biedermann's murder so that they can incriminate me. They might even have guessed I'd make Biedermann NATO sacred – it's been done before: we all know that – and now they want to pin his murder on me.' There were all sorts of other things – from the black girl's clumsy approach, to MacKenzie's murder – that supported my theory but I had no intention of revealing those. 'The whole thing adds up to a way of making me run.'

'That's what physicians call a "waste-paper basket diagnosis",' said Bret. 'You throw all the symptoms into the pot and then invent a disease.'

'Then tell me what's wrong with it,' I said.

'I'd want to see you completely cleared of suspicion before I started racking my brains about why they might be framing you,' said Bret. 'And we've still got a long way to go on that one.'