The Kreuzberg, the Hill of the Cross, lies to the south of the city, in Viktoria Park, near Tempelhof Airport. It’s where Berlin’s artists gather to sell their pictures. Just a block away from the park, Chamissoplatz is a square surrounded by high, grey, fortress-like tenements. Pension Tillessen occupied the corner of Number 17, but with its closed shutters pasted over with Party posters and KPD graffiti, it didn’t look as though it had been taking guests since Bismarck grew his first moustache. I went to the front door and found it locked. Bending down, I peered through the letter-box, but there was no sign of anyone.

Next door, at the office of Heinrich Billinger, ‘German’ Accountant, the coalman was delivering some brown-coal briquets on what looked like a bakery tray. I asked him if he could recollect when the pension had closed. He wiped his smutty brow, and then spat as he tried to remember.

‘It never was what you might call a regular pension,’ he declared finally. He looked uncertainly at Inge, and choosing his words carefully, added: ‘More what you might call a house of ill-repute. Not a regular out-and-out bawdy house, you understand. Just the sort of place where you used to see a snapper take her sledge. I remember as I saw some men coming out of there only a couple of weeks ago. The boss never bought coal regular like. Just the odd tray here and there. But as to when it closed, I couldn’t tell you. If it is closed, mind. Don’t judge it by the way it looks. Seems to me as how it’s always been in that state.’

I led Inge round the back, to a small cobbled alleyway that was lined with garages and lock-ups. Stray cats sat mangily self-contained on top of brick walls; a mattress lay abandoned in a doorway, its iron guts spilling on to the ground; someone had tried to burn it, and I was reminded of the blackened bed-frames in the forensic photographs Illmann had shown me. We stopped beside what I took to be the garage belonging to the pension and looked through the filthy window, but it was impossible to see anything.

‘I’ll come back for you in a minute,’ I said, and clambered up the drainpipe at the side of the garage and onto the corrugated iron roof.

‘See that you do,’ she called.