'All right?' Johnny asked. He'd appointed himself to the role of my guardian in exchange for the German lessons I gave him. I don't know which of us had the best out of that deal: I suspect that neither of us gained anything. He'd arrived in East Berlin a zealous Marxist but his faith had not endured the rigours of life in the German Democratic Republic. Now, like so many others, he had moved to the West and was reconstructing a philosophy from ecology, pop music, mysticism, anti-Americanism and dope.

'Yes, thanks, Johnny,' I said. 'I'm just going to bed.'

'There is someone to see you,' said Johnny.

'At four in the morning?' said Werner and glanced at me.

'Name?' I said.

Suddenly there was a screech from across the courtyard. A door banged open and a man staggered out backwards and fell down with a sickening thud of a head hitting the cobbles. Through the dirty window I could see by the yellow light from an open door. A middle-aged woman – dressed in a short skirt and bra – and a long-haired young man carrying a bottle came out and looked down at the still figure. The woman, her feet bare, kicked the recumbent man without putting much effort into it. Then she went inside and returned with a man's hat and coat and a canvas bag and threw them down alongside him. The young man came out with a jug of water and poured it over the man on the ground. The door slammed loudly as they both went back inside.

'He'll freeze to death,' said the always concerned Werner. But even as he said it the figure moved and dragged itself away.

'He said he was a business acquaintance,' continued Johnny, who remained entirely indifferent to the arguments of the Silesian family on the other side of the yard. I nodded and thought about it. People announcing themselves as business acquaintances put me in mind of cheap brown envelopes marked confidential, and are as welcome. 'I told him to wait upstairs with Spengler.'

'I'd better see who it is,' I said.

I plodded upstairs. This sort of old Berlin block had no numbers on the doors but I knew the little musty room where Spengler lived. The lock was long since broken. I went in. Spengler – a young chess-playing alcoholic who Johnny met after being arrested at a political demonstration – was sitting on the floor drinking from a bottle of apple schnapps. The room smelled noticeably more foul than the rest of the building. Sitting on the only chair in the room there was a man trying not to inhale. He was wearing a Melton overcoat, and new string-backed gloves. On his head he had a brown felt hat.

'Hello, Bernd,' said Spengler. He wore an earring and steel-rimmed glasses. His hair was long and very dirty. His name wasn't really Spengler. No one knew his real name. Rumours said he was a Swede who exchanged his passport for the identity papers of a man named Spengler so that he could collect welfare money, while the real Spengler went to the USA. He was growing a straggling beard to assist the deception.

'You looking for me?' I asked the man in the hat.

'Samson?' He got to his feet and looked me up and down. He kept it formal. 'How do you do. My name is Teacher. I have a message for you.' His precise English public school accent, his pursed lips and hunched shoulders displayed his distaste for this seedy dwelling, and perhaps for me too. God knows how long he'd been waiting for me; top marks for tenacity.

'What is it?'

'I…'

'It's all right,' I told him. 'Spengler's brain was softened by alcohol years ago.' A dazed smile crossed Spengler's white face as he heard and understood my words.

The visitor, still doubtful, looked round again before picking his words carefully. 'Someone is coming over tomorrow morning. Frank Harrington is inviting you to sit in. He guarantees your personal freedom.'

'Tomorrow is Sunday,' I reminded him.

'That's right, Sunday.'

'Thanks very much,' I said. 'Where?'

'I'll collect you,' said the man. 'Nine o'clock?'

'Fine,' I told him.

He nodded goodbye without smiling and eased his way past me, keeping the skirt of his overcoat from touching anything that might carry infection. It was not easy. I suppose he'd been expecting me to shout with joy. Anyone from the Field Unit – even a messenger – must have sniffed out something of my present predicament: disgraced ex-field agent with a warrant extant. Being invited to the official interrogation of a newly arrived defector from the East brought an amazing change of status.

'You're going?' Werner asked after the front door banged. He was watching over the balcony to be sure the visitor actually departed.

'Yes, I'm going.'

'It might be a trap,' he warned.

'They know where to find me, Werner,' I said, making him the butt of my anger. I knew that Frank had sent his stooge along as a way of demonstrating how easy it was to pick me up if he felt inclined.

'Have a drink,' said Spengler, from where he was still sprawled on the floor. He pushed his bent glasses up on his nose and prodded the buttons on the machine he was holding so that the little lights flashed. He'd finally found new batteries for his pocket chess computer and despite his alcoholic daze he was engaging it in combat. Sometimes I wondered what sort of genius he would be if he ever sobered up.

'No thanks,' I said. 'I've got to get some sleep.'

Take me to a safe house blindfolded and I'd know it for what it was. Werner once said they smelled of electricity, by which he meant that smell of ancient dust that the static electricity holds captive in the shutters, curtains and carpets of such dreary unlived-in places. My father said it was not a smell but rather the absence of smells that distinguishes them. They don't smell of cooking or of children, fresh flowers or love. Safe houses, said my father, smelled of nothing. But reflexes conditioned to such environmental stimuli found hanging in the air the subtle perfume of fear, a fragrance instantly recognized by those prone to visceral terror. Somewhere beyond the faint and fleeting bouquet of stale urine, sweat, vomit and faeces there is an astringent and deceptive musky sweetness. I smelled fear now in this lovely old house in Charlottenburg.

Perhaps this young fellow Teacher smelled something of it too, for his chatter dried up after we entered the elegant mirrored lobby and walked past the silent concierge who'd come out of the wooden cubicle from where every visitor was inspected. The concierge was plump, an elderly man with grey hair, a big moustache and heavy features. He wore a Sunday church-going black three-piece suit of heavy serge that had gone shiny on the sleeves. There was something anachronistic about his appearance; he was the sort of Berliner better suited to cheering Kaiser Wilhelm in faded sepia photos. A fully grown German shepherd dog came out of the door too. It growled at us. Teacher ignored dog and master and started up the carpeted staircase. His footfalls were silent. He spoke over his shoulder. 'Are you married?' he said suddenly as if he'd been thinking of it all along.

'Separated,' I said.

'I'm married,' he said in that definitive way that suggested fatalism. He gripped the keys so tight that his knuckles whitened.

The wrought-iron baluster was a delicate tracery of leaves and flowers that spiralled up to a great glass skylight at the top of the building. Through its glass came the colourless glare of a snow-laden sky, filling the oval-shaped stairwell all the way down to the patterns of the marble hall but leaving the staircase in shadow.

I had never been here before or even learned of its existence. As I followed Teacher into an apartment on the second floor I heard the steady tapping of a manual typewriter. Not the heavy thud of a big office machine, this was the lighter patter of a small portable, the sort of machine that interrogators carry with them.