The block was eerily quiet. Most of the residents wouldn’t have returned from work yet. As she climbed the steps, the drum beat of her footfall triggered a memory in Müller’s head about the name Sonnenstein – she’d heard it somewhere before, she was sure, she just couldn’t recall it from the back of her mind. As her footsteps echoed in the darkness, she began to wonder if it had been a good idea to come on her own – especially if it was some sort of set up by the Stasi. She should have brought Tilsner with her. But then she’d never trusted him as fully since all the events at Gardelegen, and the knowledge of what he’d been involved in during the war. His membership of the Hitler Youth, even though virtually all boys of a certain age had been members of the young people’s wing of the Nazi Party.

As she turned the corner into the third-floor corridor, she realised thinking of the Nazis had unblocked that memory of Sonnenstein. And recalling why she remembered it made her shiver. It was from one of her father’s anti-fascist rants. An example of the barbarity of the Nazis. That was what had happened here – somewhere near here, anyway. In Sonnenstein, before these apartments were built for the workers of the Workers and Peasants Republic, there’d originally been a sanatorium for the mentally ill here. For its time, it had been forward thinking – that must have been where the Dr Pienitz mentioned by the bus driver worked, whom the park outside was named after. But that self-same sanatorium in the Nazi era became the site of atrocities. Sonnenstein had been a Nazi euthanasia centre: known as the National Socialist Killing Institution Sonnenstein. The thought made Müller’s skin crawl. She was so wrapped up in it, she almost failed to notice the snowy footprints in the unheated corridor – leading right to apartment 315, her destination.

Lotti’s flat.

Someone was at home.

For some reason, perhaps some sixth sense, Müller deliberately quietened her footfall. She had an inkling something was wrong. She tried to approach as quietly as possible, but she could hear her own breathing, see the cloudlets of condensation in the cold air in front of her, and hear her heartbeat hammering in her ears.

When she reached the door to 315, and saw the splintered wood of the forced lock, she realised she was right. Someone had got here before her.

Slowly, she drew her Makarov from her shoulder holster and released the safety catch.

She pushed at the now unlocked door, opening it a millimetre at a time, hoping with every little push that it wouldn’t suddenly squeak on its hinges.

When it was fully open, she advanced equally slowly into the dark interior of the apartment, holding her gun pointed in front of her in both hands, finger ready on the trigger.