Marcus Klingberg, who died in Paris in 2015 after 20 years in prison in Israel, was his country's most dangerous spy. A Polish Jew who joined the Red Army to escape the Holocaust and a veteran of Israel's independence, Professor Klingberg was for thirty years the head of Israel's secret bacteriological weapons program. No one suspected at the time that he was the KGB's number one mole. Klingberg's secret motives are explored through the recordings of his confessions and the testimonies of those who worked with him as well as the leaders of the Israeli secret service who arrested him.