Olga finds her husband Karel Brand, whom she has just divorced, shot dead after returning from the cinema. It appears to be a clear case of suicide, but Lieutenant Dusek of the Public Security Service suspects that it is a murder, which, it is not impossible, as a number of evidences point against it, could have been committed by Mrs Olga. A letter from the dead man to his wife seems to dispel any doubt that it could have been murder. Lieutenant Dusek, however, investigates further. Much more than he, however, learns about the true circumstances from Mrs. Olga's legal advisor, Dr. Klimesh. He learns that the letter is indeed a forgery and that Brand's death is linked to the raids of an anti-state gang. He hesitates for a long time whether to confide in security, believing that doing so would testify in favor of Dusek's theory that the murder was committed by Olga...