Prague 1942. Following the assassination of Nazi "Reich Protector" Heydrich, Masha Novotny, a professor's daughter, hides the culprit in her parents' apartment. When the Gestapo take 400 people hostage in retaliation, Masha's father is among those arrested. The assassin, surgeon Dr. Svoboda, manages to escape. As they search for him the Gestapo also train their sights on Masha. While hostages are being executed daily, she helps Svoboda in his efforts to blame the assassination on a collaborator and save her father's life.