Two security guards grappled Kiraly to the ground. Another man, perhaps one of the organisers, rushed over to assist. As Kiraly’s face was pushed against the floor, his eyes flicked with terror, before a hand swam up to the camera lens and the film cut out.

Gessen stared at the darkened screen, his heart bumping against his ribs. In need of air, he raised the blinds and flung open the window, hoping the sight of the high mountains and vast bowl of open space would settle his churning thoughts.

The raw fury in Kiraly’s face. So unexpected in such an elegantly dressed and courtly Cambridge don. Why the explosive rage, and at that particular man? Was it someone Kiraly knew, or believed he did? It didn’t make sense. Gessen’s first thought was amok syndrome. From the Malay word for ‘rampage’, the rare, delusional condition was characterised by non-premeditated violent or homicidal rage against another person or persons. He’d never seen a real case up close, but it had fascinated him since his medical school days. Often accompanied by amnesia or exhaustion, an individual afflicted with amok syndrome might be driven to psychotic rage by something as trivial as a perceived insult.

He had some experience with similar bizarre disorders. Years ago, he’d treated a young boy with lycanthropy, a rare delusion that one was turning into an animal, such as a wolf. In the case of Gessen’s patient, it wasn’t a wolf but a lynx. The boy was from Romania and, according to his mother, he was frightened by a lynx as a toddler, and had acted strange ever since. Then there was the woman from Korea whom he’d diagnosed with shin-byung, a delusional disorder with symptoms of anxiety, dizziness, and gastrointestinal complaints. The patient believed she was possessed by ancestral spirits and such was her distress that even now, six years later, he could recall the terror in her eyes and her piercing screams.

An older woman with Capgras was a particularly heartbreaking case, one of his first as a trainee doctor in Zurich. A truly bizarre disorder, also known as imposter syndrome, in which family members or friends appear either as strangers or are mistaken for each other. The woman had become convinced her husband of thirty-five years was her long-deceased father and refused to let him sleep in her bed. Diagnosed with atypical psychosis, she only recovered after spending several weeks at a psychiatric facility in the high mountains near the Austrian border.