It seemed these people had an inkling of what was going on in their neighbourhood. Fortunately their main reaction was to act surly and not get involved. Perhaps they would not be in a hurry to give information to the police or the Nazi party.

Carla and Frieda went farther along the street and found the youth hostel. There were thousands of such places in Germany, designed to cater for exactly such people as they were pretending to be, athletic youngsters on a vigorous open-air holiday. They checked in. The facilities were primitive, with three-tiered bunk beds, but the place was cheap.

It was late afternoon when they cycled out of town. After a mile they came to a left turn. There was no signpost, but the road led uphill, so they took it.

Carla’s apprehension intensified. The nearer they got, the harder it would be to seem innocent under questioning.

A mile later they saw a large house in a park. It did not seem to be walled or fenced, and the road led up to the door. Once again there were no signs.

Unconsciously, Carla had been expecting a hilltop castle of forbidding grey stone, with barred windows and ironbound oak doors. But this was a Bavarian country house, with steep overhanging roofs, wooden balconies, and a little bell tower. Surely nothing as horrible as child murder could go on here? It also seemed small, for a hospital. Then she saw that a modern extension had been added to one side, with a tall chimney.

They dismounted and leaned their bikes against the side of the building. Carla’s heart was in her mouth as they walked up the steps to the entrance. Why were there no guards? Because no one would be so foolhardy as to try to investigate the place?

There was no bell or knocker, but when Carla pushed the door it opened. She stepped inside, and Frieda followed. They found themselves in a cool hall with a stone floor and bare white walls. There were several rooms off the hall, but all the doors were closed. A middle-aged woman in spectacles was coming down a broad staircase. She wore a smart grey dress. ‘Yes?’ she said.

‘Hello,’ said Frieda casually.

‘What are you doing? You can’t come in here.’

Frieda and Carla had prepared a story. ‘I just wanted to visit the place where my brother died,’ Frieda said. ‘He was fifteen—’

‘This isn’t a public facility!’ the woman said indignantly.

‘Yes, it is.’ Frieda had been brought up in a wealthy family, and was not cowed by minor functionaries.

A nurse of about nineteen appeared from a side door and stared at them. The woman in the grey dress spoke to her. ‘Nurse König, fetch Herr Römer immediately.’

The nurse hurried away.

The woman said: ‘You should have written in advance.’

‘Did you not get my letter?’ said Frieda. ‘I wrote to the Senior Physician.’ This was not true: Frieda was improvising.

‘No such letter has been received!’ Clearly the woman felt that Frieda’s outrageous request could not possibly have gone unnoticed.