Only in March 1950 did he again attempt his mission, this time in camouflage and accompanied by a secret guide. After holing up in a safe house on a farm owned by the anti-communist Tous family, Dvoracek travelled to Prague, again seeking Vaclavik. The person he found, however, was Militka, whom he hadn't seen in over a year. She was by now enrolled at Charles University, living in the Kolonka residence hall, which doubled as a salon for budding socialist intellectuals. Though Militka wasn't a party member herself, her current boyfriend, a student named Miroslav Dlask, was. The two had met at a student work camp where Dlask, the son of an Auschwitz survivor, impressed Militka with his prophesies of how social democracy would fuse seamlessly with communism and usher in a new age of humanism.

Someone who shared Dlask's views, albeit with a greater degree of self-criticism, was an extraordinarily gifted film student named Milan Kundera, who was already known among the leftist intelligentsia in Prague as a café-haunting prodigy, ever questioning and heterodox in Marxism. He had joined the party in his youth, writing poems and songs about proletarian revolution that have justly been forgotten. But like his future character Sabina in The Unbearable Lightness of Being he loathed May Day parades. "He was a reserved sort of person and had no liking for stupid mass rallies," his friend Milan Uhde told Adam Hradelik (the researcher whose sleuthing later uncovered the whole affair). "I tended to think of him as someone with courage who wasn't afraid to express inconvenient opinions." So when Dvoracek found Militka again, it's safe to say she was keeping dangerous company. "I was immensely pleased to see him," she recounted. "I didn't give it much thought. I asked Miroslav how Juppa was and then he walked me back to the hall of residence. He asked me if he could leave his case there for a couple of hours. He told me he had some things to sort out in Prague and he'd come back for it in the afternoon."

Dvoracek never found his chemical engineer. When he returned to Kolonka later in the evening to retrieve his briefcase - which, by the way, contained nothing incriminating - two armed policemen were waiting for him. He was arrested, interrogated and probably tortured. According to security archives, Dvoracek probably refused at first to give up the identities of his associates in Czechoslovakia, including the keepers of the safe house. He also protected Militka and her family. In September 1950, Dvoracek was convicted of desertion, espionage and high treason. He received a sentence of 22 years' hard labour, a 10,000 crown fine, the forfeiture of all his property and the suspension of his civic rights for a decade. Meanwhile, whether because Dvoracek ultimately did confess, or because the secret police had obtained further evidence independently, the Touses were arrested. Josef Tous, the youngest, received 10 years' imprisonment, others 20 years. One guide on the farm that had sheltered Dvoracek was executed. Between 1952 and 1963, Dvoracek was confined to a small, unheated concrete cell. He mined uranium, took part in a famous hunger strike and was several times penalised for violating camp regulations, such as "inciting" slogans, reading an English detective novel and studying the English language.

Miroslav Dvoracek, the spy who was imprisoned for 14 years after allegedly being betrayed to the Czechoslovak police (Getty)