In an attempt to escape his past as an informer for the German Democratic Republic's Stasi, Helmuth Busch goes to Mexico in 1971. However, he is recognised by the Mexican secret service who blackmail him. Anxious to avoid being deported, he accepts a dangerous proposition put to him by Mexican secret service chief Diaz, which involves Busch keeping a close eye on a group of politically active students. Using the undercover name of Bruno Muller, Busch is made visiting professor of history at Mexico City University. In this way, Bruno comes into contact with members of the Mexican students' movement. At first, Bruno Muller keeps his distance from the students. However, his situation becomes increasingly complicated when he starts getting more involved with the activists and his affair with a young student named Adela begins to get serious. And then, when Diaz orders him to kill the leader of this revolutionary cell, Jose, Bruno Muller is faced with an impossible dilemma...