Exiled from the Soviet Union in 1929, Leon Trotsky travels from Turkey to France to Norway, before arriving in Mexico in January 1937. The film begins in Mexico City in 1940, during a May Day celebration. Trotsky has not escaped the attention of the Soviet dictator of the Soviet Union, Joseph Stalin, who sends out an assassination named Ramón Mercader. The killer decides to infiltrate Trotsky's house by befriending one of the young communists in Trotsky's circle.