In the end, it was Bahlow himself who settled the matter. He must have overheard part of what Southwick had said. ‘I can help if you like. As you no doubt know, myself and some of my fellow agents posed as builders while we were staking out the murder scene at the start of all this. I’ve still got my hard hat and overalls in the boot. And some tools. I might be able to provide the cover you need.’

*

Once Bahlow had kitted himself up, they strolled towards the pub and located the foundation stone in the wall. No one seemed to be paying them a second glance, but Bahlow made play of preparing a chisel and hammer, as though he was doing something official.

Meanwhile, Müller ran her fingers round the edge of the stone, trying to find if any papers had been slipped into the cracks.

No luck.

There were no gaps. The area around stone had been freshly pointed – which seemed to imply someone had indeed recently tampered with it. Bahlow’s skills as a construction worker would need to be put to the test.

‘Do you think you can get it out, or at least loosen it?’ she hissed into the Stasi man’s ear, while Tilsner put his body in the way to try to shield what they were attempting to do from prying eyes.

‘I can have a go,’ replied Bahlow, as he began to chip away at the mortar.

It didn’t take him more than a few minutes to loosen the stone. He gestured for Tilsner and Müller to swap places, and for Müller’s deputy to help him lift it out.

Müller knew she was supposed to be keeping guard, but she couldn’t help sneaking looks behind her. The two men gave one final heave and pulled the stone out. As they did so, Müller turned and moved forward.

The resulting cavity seemed empty, save for small pieces of concrete and mortar debris. Frantically, she ran her gloved hand round it – searching for something, anything.

‘Scheisse!’ Swearing was more Tilsner’s forte, but she felt a horrible cloud of disappointment settle over her. But just as soon as it did, her mind started working again. The stone had been tampered with. It must have been, that’s why the mortar was fresh. Without waiting to explain what she was doing to Bahlow and Tilsner, she raced towards the pub entrance. Once inside, she sought out the manageress they’d talked to about the drunk that Jäger had tried to claim was Concrete Man. She remembered the woman’s apparent desire to bore them with the explanation of the pub’s name.

Müller flashed her Kripo ID, although the woman clearly recognised her.

‘The foundation stone outside. When was it laid?’