When they were back at the People’s Police HQ – Schmidt having bagged up what he could from the underground den, and taken fingerprints from likely objects that couldn’t be moved – Müller called an informal meeting in her office.

‘Let’s go through what we’ve got to go on now,’ she said.

‘Not a lot,’ grumbled Tilsner, who Schmidt had said was showing no signs of concussion. ‘Considering how long we’ve been going round chasing our own tails.’

Müller ignored him. ‘Jonas, I want you to go through everything we’ve recovered from the drain tunnel. Check for fingerprints, clothes fibres, footprints, anything like that . . . see if you can establish who was using the hideout. Or if not who, then how many people. Was it just Lotti’s lair, or has she been helping someone hide away from the authorities?’

‘It doesn’t make much sense,’ said Tilsner. ‘Why would you build a hideout there, on the edge of Dresden, near the Elbe? Wouldn’t you choose somewhere more remote – Dresden Heide for instance?’

Again, Müller chose to ignore Tilsner. If he didn’t have anything positive to contribute, then she wasn’t going to listen to him. ‘Have you found anything of interest from your initial sift-through, Jonas?’

‘There was one thing, yes, Comrade Hauptmann,’ said the forensic officer. ‘An expired works pass for SDAG Wismut in Königstein. In Lotti Rolf’s name.’

‘She was a uranium miner?’ asked Müller. That was hard to believe.

‘Not a miner, no,’ said Schmidt. ‘Although there are a minority of female miners. No, she worked as part of the administration of the mine.’

‘Worked or works?’ asked Tilsner.

‘I’ve no idea, Comrade Oberleutnant. All I can tell you is that she possessed an out-of-date pass.’

‘When did it expire?’ asked Müller.

Schmidt consulted his notes. ‘December thirty-first last year – so only a couple of months ago.’

Müller got to her feet and retrieved her coat from the back of the office door. ‘Werner, you come with me. Let’s pay the mine a visit. At least it’s something to be going on with. Jonas, you go through the rest of the stuff please and, as I say, try to find out exactly who was using the lair in the Elbe water meadows.’

*

The contrast between the two sets of hills was striking: the beauty of the Elbe Valley, and the historic town of Königstein itself, with its imposing castle named after the king of Bohemia; and the moonscape and slag heaps of SDAG Wismut. Müller wasn’t entirely sure why the enterprise had that name. Perhaps it was one of the Republic’s many euphemisms, a little like the Anti-Fascist Protection Rampart. Wismut – or bismuth – did sound somehow much less frightening than uranium, which was known to be used in the Soviet Union’s nuclear weapons.