In the half-light and shadows of street lamps and new and partially built apartment blocks, they followed Bahlow as he picked his away along wooden duckboards – the makeshift paths that had been threaded between the piles of building materials, muddy waste ground, and the new-builds themselves.

Müller led the way for her and Tilsner, making sure she stayed some twenty metres or so behind the Stasi officer. Both of them knew this might be another trap, or another piece of gaming. But each of Bahlow’s tips – or deliberately planted pieces of evidence, if he was responsible for those too – had so far advanced the case. Müller had weighed it up in her head, as she was sure Tilsner had too. They had little to lose, and everything to gain.

Bahlow’s weaving, seemingly tortuous route had taken them to a part of the residential area which – although newly built – almost appeared to have been abandoned, at least temporarily. The apartment blocks were just shells – no windows, no doors, no street lights. The concrete blocks rose like ghostly shapes in the gloom, the slightly lighter colour of the concrete fractionally picked out by the ambient light of the centre of Dresden, in the valley a few kilometres to the east. In the dim light, Müller could make out a street sign – Amelie-Dietrich-Platz – and a sign below explaining that the woman had been a nineteenth-century botanist and explorer.

Then – in one of the empty shells – a flickering light from one of the windowless openings on an upper floor. Bahlow had stopped and was pointing to it. Müller counted the floors as her head panned upwards – one, two, three . . . thirteen, fourteen, fifteen. Just one floor before the very top.

She turned back, intending to draw closer to Bahlow to ask him what this was all about.

But he’d disappeared into the night.

Slipped away behind the pipes, blocks and construction material, some of which were already weed-infested – as though the site hadn’t been touched for weeks.

She looked back up to the fifteenth floor and the dim, flickering light. Then glanced at Tilsner, drew close, and cupped his ear.

‘We’re going to have to go up,’ she whispered. ‘He’s clearly brought us here for a reason.’

She could sense Tilsner’s reluctance. ‘Yes, but what reason?’ he hissed. ‘Probably to do exactly the same to us as they did to the director of the sports school at the TV tower.’

Müller drew back from him, aghast. ‘What makes you think that wasn’t suicide? There was no indication of foul play.’

‘Except for those documents the laundry woman gave us. Has Schmidt managed to decipher them yet?’

‘He’s been busy with other stuff. But I will chase him up about it.’