Le Secret, based on a novel by Francis Ryck, begins with the escape of mental patient David Daguerre (Jean-Louis Trintignant), who kills an asylum guard in the process. Daguerre hides out in the home of writer Thomas Berthelot (Philippe Noiret), explaining that his wounds and bruises are the result of torture at the hands of the "special police." Berthelot and his wife, Julia (Marlène Jobert), are willing to believe that Daguerre is a fugitive from oppression, especially after their house is surrounded by a group of soldiers on maneuvers. The couple tries to help David escape to Spain, but Julia, who during most of the proceedings has been attracted to the escapee, becomes convinced that Daguerre is insane and kills him in self-defense. The surprise ending leaves the audience wondering whether or not the man had been telling the truth all along.