 In 1930, Maria Brentano (Valentina Cortesa) and her younger sister Nora (Audrey Hepburn) flee to London after their father is murdered by a European dictator. Seven years later, during a weekend trip to Paris, Maria unexpectedly meets Louis (Serge Reggiani), her former lover who is now plotting the assassination of the dictator. Maria and Nora become involved in the plan, which goes tragically wrong when the time bomb they plant kills an innocent bystander.