A stranger enters into and forever alters the life of a couple. He claims to be pursued by certain authorities who intend to prevent him from disclosing a secret that only he holds, whence the title. Is he lying, or insane - or is he telling the truth? Who, if anyone, is after him? And what *is* - the secret?
Jean-Louis Trintignant, Marlène Jobert, Philippe Noiret, Jean-François Adam, Solange Pradel, Antoine Saint-John, Michel Delahaye, Maurice Vallier, Frédéric Santaya, Jean-Claude Fal, Patrice Melennec, Pierre Danny