Gerd Keil is afraid of basements. He is also afraid of metallic scraping sounds, aggressive male voices and a certain East German dialect. Any of these can reduce Keil, a towering 51-year-old Berliner who looks as though he could fell an ox with his bare hands, to a sweat-drenched, trembling wreck. The panic attacks are a result of his time as a young political prisoner in the GDR in the 1980s, after an attempt to flee to the west. He was locked away for three years after 10 informants betrayed him to the Stasi, East Germany’s feared secret service. Two of these informants were particularly active. It was not until the 1990s that Keil found out their identity: one of the two was his own father.

“And the other?” I ask. We are sitting in a house in a leafy suburb of Berlin, accompanied by a therapist and Keil’s partner, Manuela. Keil pauses. His partner places a protective hand on his arm.

“My brother,” he replies. His body is gripped by a brief, violent spasm, painful to watch. Keil’s brother is not named in his file, but referred to by a Stasi code name; his reports contain information Keil says only he and his brother knew.