East German dissident Alex Holbeck (Martin Sheen), living in Paris, hosts a radio program aimed at Iron Curtain countries. Bodley (Michael Lonsdale), a CIA agent, recruits Alex to take on a dangerous assignment.
Alex is sent to East Berlin on a mission to steal an Enigma code scrambler. This is part of an attempt to stop the Russian assassination of five Soviet dissidents planned for Christmas Day. Alex does not know is that the CIA already has a code scrambler. By stealing the scrambler in Berlin, they are trying to convince the Russians that they do not have a copy.
On arrival in Berlin, Alex finds that the East German police and KGB knows that he is there. Alex must use numerous disguises and escape from a number of capture attempts. He seeks shelter with his former lover, Karen Reinhardt (Brigitte Fossey), before moving on, as it is too dangerous for her. Karen and a number of Alex's other old friends are arrested and tortured by the police in an attempt to gain information about Alex's whereabouts.
As he gets more desperate, Alex enlists Karen's help again; she seduces Dimitri Vasilikov (Sam Neill), the KGB man in charge of the hunt for Alex, to obtain information. In the end, Dimitri catches Alex and Karen and finds the scrambler hidden in an exhibition artifact. As he is in love with Karen, he lets them go, but keeps the scrambler, which was in fact not needed. On Christmas Day, the assassination attempt is successfully thwarted.
