Ursula burst through the door, waving an envelope over her head. ‘Wait till you read this,’ she said. ‘You won’t believe it.’

She was gasping for breath as if she’d run all the way across the grounds. He took the letter, mildly alarmed by her flushed face. It was addressed to Dr Ursula Lindstrom, with the word ‘confidential’ written on the envelope in block letters with a red marker. Clearly impatient for him to read it, she perched on the arm of the chair.

As the contents of the letter sunk in, he met her gaze. It was sent by the former house attendant at Chalet Est, a man named Aleks, who had gone home to Slovenia in a hurry to care for his sick mother. Or so he said. But now it appeared he had another reason for leaving the clinic. In the time since his departure, his conscience must have got the better of him, and he now wished to confess. Apparently, Vidor had asked Aleks to help him with an experiment.

According to the letter, it went like this: Aleks would remove Vidor’s wrist monitor, with the aid of a special device, and place it on his own wrist. He would then lie down on the floor of Vidor’s bedroom and hold his wrist to his forehead and remain there quietly for thirty minutes. Vidor had told Aleks that he was a prize-winning brain scientist, and that he needed Aleks’ help to prove a theory that people who lived in close quarters were able to synchronise their brain waves. I realise, it was wrong of me, Aleks wrote in a scratchy hand, but it seemed like such a good idea and I didn’t want to disappoint Mr Vidor. He said I was doing him a great service in understanding the brain, and that he would mention my name in the article he published of the results.

Gessen looked at Ursula. ‘Good grief.’

She shook her head. ‘It gets worse.’

Only later did I realise I had helped Mr Vidor with his experiment on the day that Mr Ismail went missing. So, the reason I am writing to you is to tell you that the information on Mr Vidor’s patient log is not correct. I don’t think he did anything wrong, but ever since I left the clinic, it’s been bothering me. I hope you will forgive me for not telling you sooner, and I am sending you this information now with the hope it will not change any facts about the day Mr Ismail died.

Gessen set his reading glasses on the desk. ‘Why do you suppose he sent this to you, and not me?’

‘I don’t know.’ She hesitated. ‘Maybe he hoped I wouldn’t say anything.’ Ursula twisted the ring on her finger. ‘But we’ll have to inform the police now.’