Mannix works with a police detective to find the reasons behind the death of Peter Martin. When Mannix accuses Carlos Valera, the private eye takes on more trouble than he bargained for. After Valera's arrest, Mannix begins to have doubts about his guilt and begins digging further into the case despite hostility from Valera's neighbors as well as Martin's sister.

Mannix is left holding the bag when he's hired by Pete Neal, a man he knows, to protect a man with $25,000 that they both claim isn't stolen. Neal is killed, and Neal's body, the man, and the money disappear.

Mannix becomes involved in murder and political intrigue when he helps newspaper publisher Jason Walker finds out the reasons for the strange behavior of his daughter Diana. The case rekindles a romance between Mannix and Diana, as he tries to prove that she is being framed in the hit-and-run death of an underworld figure.

Mannix almost loses Peggy when he tells her that he suspects her new boyfriend, Floyd Brown, of being the key man in the theft of forty-five cartons of morphine. Caught between her loyalty to Mannix and her love for Brown, Peggy refuses to listen to Mannix but later places her life in danger when she confronts Brown with the accusation.

Mannix is hired to track down a compulsive gambler hunted by loan sharks.

A neighbor drops in via a window, asks Mannix to release a man in his office, and then runs off with men in pursuit, and Mannix discovers that the neighbor's business is a front.

A Korean War vet takes Lt. Malcolm hostage and booby-traps an entire building to lure Mannix to him.

Peggy asks Mannix to help find her new boyfriend, who fled a music club without a word when he saw a particular man in the audience.

Mannix suspects an attorney of making three murders look like suicides to cover up the attorney's own guilt.

Mannix investigates the death of a businessman who tried to kill the PI and then went berserk, claiming he was having dreams of his time in the Korean War.

A tennis pro turns up dead after trying to blackmail a gubernatorial candidate, and Mannix is hired to find the killer.

A woman is attacked in her apartment and thrown out her balcony to her death, and the police conclude that it is a suicide thanks to a forged suicide note Mannix believe she was murdered and investigates the death.

The owner of a jewelry shop is murdered. When Mannix arrives at the crime scene, he runs into an old friend from his days in the Korean War who asks him to visit a small mountain town where he can gain information on the situation.

Mannix is brought to a small town in New Mexico under false pretenses, where he is then served a subpoena and must testify as an expert witness for the prosecution in a murder trial; he stays on the trial as the aid to the defense.

While on a helicopter ride to Santa Barbara, Mannix witnesses a man strangling a woman on a penthouse terrace. However, when he investigates, the occupants of the penthouse say that there has been no foul play.

Cliff Ross, Jr. awakens in big trouble. A girl is dead, there's evidence he was in some kind of fight and he can't remember what actually happened. Unless Mannix can help him reconstruct events, he's likely to go to prison.

The first crook that Mannix put away asks for his help to prove his innocence seven years later.

A millionaire's ex-wife is supposedly dead, but he claims that he saw her alive and hires Mannix to find her.

Kidnappers promise to kill a doctor's son unless he lets a patient die on the operating table.

A publisher hires Mannix to find the missing last chapter that an author was working on before his boat was blown up.

Mannix tries to determine why an ex-con on parole was coming to see him.

While participating in an amateur auto race, Mannix witnesses a competitor's death. The driver's widow subsequently hires Mannix to confirm the death was a homicide.

Hoods abduct a young man who comes to Mannix for help, then try to buy the PI off... all as part of a scheme to influence a judge.

A former cop turned airport security guard who saved Mannix's life years before hires the PI to find his missing wife Rose, but then changes his mind. Despite that, Mannix probes further to find out why.

After leaving Intertect to start his own agency, Mannnix's first case involves a deaf woman who "overhears" an assassin's phone call by reading his lips, and tries to tell the police what she knows.