Once they reached the tourist tram’s valley terminus, they parked the car. Müller again glanced back along the road. The Lada had pulled into a lay-by some two hundred metres or so behind them – its occupants showing no inclination to follow them on foot.

‘They’re just on a watching brief, I expect,’ said Tilsner.

Müller took in their surroundings. The tram terminus platform was covered in snow, with only a few footprints stamped out on its white blanket. Clearly in winter – or at least in this weather – Kirnitzschtal wasn’t a huge draw. As Lotti’s mother had predicted, the inn opposite was closed and looked half-abandoned.

They tried to get their bearings from the old woman’s descriptions, looking for the signs for the waterfall. Just a few metres along the track, before the falls themselves, there was what looked like the ‘cottage’ – though to Müller’s eyes, to call it that rather overstated things. The single-storey building looked more like a run-down weekend allotment shed.

Tilsner rapped hard on the door. No response. He made to give it a kick before Müller held up the key admonishingly. She leant on the door as she made to unlock it, but before she had inserted the key, the door swung open freely.

‘Frau Rolf!’ shouted Tilsner as they stepped inside. ‘Are you in? It’s the police. The K.’

There was silence, save for the dripping of a tap in the kitchenette.

Müller scanned the work surfaces. There was a half-drunk mug of coffee on the draining board. She clasped her hands around it.

Still warm.

Someone had been here – perhaps within the last fifteen minutes. She handed it to Tilsner.

‘So – if it’s Lotti, where’s she gone?’ he asked.

Müller didn’t answer, but instead opened the cottage’s back door. Footprints in the snow – and they looked fresh.

She followed the tracks, conscious that Tilsner was close behind her, but not stopping to wait for him. The prints formed part of a narrow path through snow-covered ferns into a wooded area behind the waterfall. Müller couldn’t see it, but could hear the roar of water and knew it was nearby. It might have been cold enough to snow, but the temperatures hadn’t become low enough to actually freeze streams or rivers.

As they entered the wood, Müller realised the snow cover under the tree canopy was much thinner. Not only that, but the path – and the prints – had disappeared.

She frowned and stopped, then turned back to her deputy.

‘It’s not clear which way now,’ she said.

Tilsner peered at the ground, trying to see what had happened. It was as though the footprints had evaporated into thin air.