By resting my face close against the glass it was possible to see into the next room. There were two people there, a man and a woman. Both wore white linen: a doctor and nurse. The woman was about forty; over her greying hair she wore a small starched cap. The man was younger, twenty-five or so. His white jacket was unbuttoned and there was a stain on the lapel that might have been blood. A stethoscope hung from his neck. He stood by the door writing in a small notebook. He consulted his wristwatch and then wrote more. The nurse was leaning against a two-tier bunk bed looking at something bundled there on the lower bed. She looked back to catch the doctor's eye. He looked up from his writing and she shook her head. The movement was almost imperceptible, as if she'd been shaking her head all morning. She was Russian, I had no doubt of that. She had the fiat features, narrowed eyes, and pale colouring that are typical of people from Russia 's eastern Arctic. She turned back to the bundle of clothes and touched it tenderly. It was too small to be a person – except a very small person. She leaned closer, fussing in the way that mothers do when babies sleep face down. But this was too big for a baby. She moved a trifle. It was a child – a red woolly striped hat had slipped from its head. Swaddled in thick blankets an elbow protruded from between. A yellow sleeve – an anorak. And shiny boots. Jesus Christ, they had Billy! Little Billy. Here in Berlin.

The scene wobbled, my pulse raced, and my throat was suddenly dry. Only by steadying myself against the wall was I able to prevent myself fainting. Billy! Billy! Billy! I leaned close to the peephole again. The nurse moved away to get a small enamel tray from the table. She carried it carefully to the sink and took from it a hypodermic syringe. She put the needle into a glass of pink-coloured liquid. I felt ill. No matter how much my brain told me to remain calm, my emotions took over. Now I knew why men with wives and families were so seldom used as field agents.

They are watching, they are watching you, now, at this moment, I told myself for the hundredth time. This is all a well-prepared act to disorient you and soften you up for what comes next. But it didn't help much. I could think of nothing except my son and what these bastards might do to him. Surely to God, Fiona knows about this. Surely she would stop them hurting her own son. But suppose Fiona doesn't know?

There was the sudden noise of a key being inserted into the lock. Someone was entering from the corridor. There was enough time for me to get back to the bench and sit down. There was enough time for me to look relaxed and unconcerned, but I'm not sure I managed that.

'Herr Samson!' We knew each other. He was a great bull of a man, about fifty years old, with a big peasant frame upon which years of manual labour had layered hard muscle. His skull shone through close-cropped hair. His large nose was surmounted by a big broad forehead. Pavel Moskvin. The London Central computer described him as a KGB 'political adviser'. That could mean anything. Political advisers were sometimes the brightest of bright graduates, multilingual polymaths who could quote Groucho as readily as Karl Marx. Such men used a stretch with the KGB as a finishing school. But Moskvin was long past all that. I had him marked down as the sort of untalented plodder who'd graduated from the factory floor having discovered that the Party always looks after its own. The USSR was filled with men like him; their unthinking loyalty was what held the whole creaky system together.

'Where is my wife?' I asked him. It wasn't a textbook opening or anything that London Central would have approved, but I knew they'd have me on a tape and there seemed a good chance that Fiona would be monitoring the dialogue.

'Your wife? Why would you want to know that, Herr Samson,' said Moskvin mockingly. His German was awkward and ungram-matical but his manner said everything.

'My people know I'm here, Moskvin,' I said. They'll be putting out a red alert any time now.'

'Are you trying to frighten me?' he said. 'Your people know nothing, and they don't care. It is Christmas. You are all alone, Herr Samson, all alone. Your people in London will be eating pudding, watching your Queen speaking on television and getting drunk!'

'We'll see,' I muttered ominously, but his version of what London Central might be doing sounded only too likely.

'Why don't you behave sensibly, Samson?'

'For instance?'

There were footsteps in the corridor. He half turned towards the door, his head cocked to listen. The break in his attention gave me the chance I'd been praying for. With both hands cuffed behind me, I grasped the backrest of the chair. Then, with head bowed low to counter the weight, I twisted my body and with all my force heaved the chair in his direction.

It was too heavy for me. It hit him in the legs instead of on the side of the head, but the violence of it caught him unprepared so that he staggered back cursing and spluttering with rage.

He kicked the chair aside. 'I'll teach you…' he said and stepped forward to punch me. He didn't aim anywhere; he hit me as an angry drunk might pound a wall. But Moskvin was a heavyweight. His blows didn't have to be aimed; they hit like sledgehammers and I was slammed against the wall so hard that I lost my balance and slid to the floor. 'You crazy fool!' he growled and wiped his mouth with the reddened knuckles of his fist. 'If you want a fight I'll take you downstairs and kill you with my bare hands.'

Slowly I scrambled to my feet and he kicked the chair over to me again with the side of his boot. I sat down on it and closed my eyes. I had a terrible pain inside me, as though molten lead was pouring through my lungs.

When Moskvin spoke again, he'd recovered some of his former composure. 'Be sensible. Face the truth. Your wife has chosen to work with us of her own free will. Do you really believe that we are holding her captive? Is that what your bosses in London have told you? Forget it. She is one of us, Samson. She does not wish to return to the West; she will never go back there. Never.' He watched me carefully and I stared back at him. 'Do you want a cigarette?' he asked finally.

'No,' I said, although I needed one desperately. We both knew the way it went; you accept a cigarette, you say thank you, and the next thing you're chatting away and reaching for the writing paper, 'I don't smoke.'

He smiled. He knew all about me. With Fiona working for the KGB, there was little about me that they couldn't find out. The pain lessened a little as I shifted my position and controlled my breathing, but one of his punches seemed to have torn a ligament and the big trapezius muscle of my back sent sharp pains right up to my neck.

'Why make life miserable for both of you?' said Moskvin in what he obviously thought a friendly manner. His German was better now; perhaps this was a text he'd prepared and practised. 'While you are working for the German Stations Controller in London and your wife is here in Berlin, the two of you must be permanently unhappy.'

'What are you proposing?' I said. I tried not to look at the glass-panelled door but it was difficult. Moskvin watched me carefully. He knew I'd seen into the next room. His arrival was too prompt to be anything but a reaction from a man watching what I did. Yes, I could see it now; the camera was behind that damned anti-nuke poster. A circular patch of the lettering was dull – open-weave cloth through which a focused camera could see clearly.

'There would be nothing for you here, Samson. We know everything you could tell us.'

I nodded. Had they really given up hope of enrolling me, or was this some subtle way of trying to get me to prove I knew more than they thought. 'You're right,' I said.

'So why not an overseas posting?' said Moskvin. He had both hands in the pockets of his greatcoat, fidgeting with something metallic that clanked. When he brought his hands into view there were three clips of pistol ammunition in his ringers. He fiddled with them. When he saw me looking at him he said, 'Don't have any more of those stupid ideas, Samson. The gun is downstairs in my safe.' Lots of bullets; it was characteristic of this violent primitive.