Joe Mannix is confronted by Harry Bennett, with whom Mannix served in Korea and who was later court-martialed, on testimony from Mannix, for giving information to his captors while a prisoner of war. Bennett claims that he is going to put Mannix through the same ordeal he faced at the hands of the North Koreans, and gives Mannix a name that Bennett claims Mannix will be unable to hold back once he becomes a captive. Then Bennett's threats seem to come true when Mannix is offered a sizable sum of money for the name of an informant within an underworld organization - ...
Peggy's cousin and her husband, a Vietnam veteran named Bill Rogell, are traveling to Los Angeles by bus when Rogell runs into fellow veteran Clint Williams at a stopover. While they reminisce, Rogell thinks he recognizes another man from their unit, but Williams insists Rogell is mistaken. Joe Mannix becomes involved, however, when the couple arrive in Los Angeles and Rogell is stabbed at the bus station.
At the start of a long weekend, off to a fishing vacation with friend Tony Elliott, Mannix stops at Tonys office so Tony can pick up a set of fishing flies. They walk in on a methodical heist of the businesses in the building. Mannix is trapped in the building, playing a cat and mouse game with the three burglars.
While driving back to Los Angeles, Mannix gives a lift to a black hitchhiker named Perry Riggs. Riggs is soon arrested at a roadblock, however, and charged with the murder of his former boss, a scientist who had been working on a formula for a gasoline replacement. Mannix decides to stay in the town to investigate the circumstances of the man's death -- in the hope that he can find evidence exonerating Riggs.
Mannix travels to an island that's part of a South American country. Mannix's client wants to repay the man for the saving the life of the son of the client some years earlier. But Mannix soon discovers the case is more complicated than he bargained for. The man he's searching for is part of a plot to assassinate the president of the country. Just as Mannix is putting the pieces together, he's captured by the conspirators.
The conspirators assassinate the president of a South American country and successfully frame Mannix for the killing. Now, the detective must dodge the authorities and hunt the conspirators as he tries to clear his name.
Newspaper publisher Darrell Bigelow has political ambitions, but is concerned about the extramarital activities of his wife, Rebekah. Bigelow hires Joe Mannix to "bring her home," and Mannix is soon able to track her down. But his easy success in closing the case soon leads Mannix to suspect that Bigelow's story was a cover-up, and that he used Mannix for a different, and much darker, purpose.
A hit man shoots his victim, a notorious crime boss, from a sniper's perch, but moments later can find no body where the man fell. Unable to convince the men who hired him that the crime boss is actually dead, he concocts a story about being a witness to a shooting and hires Joe Mannix to investigate whether a man really was killed that night, and if not, what happened to him.
In the series' final show: To ensure a safe release of 6 hostages taken by a desperate drug dealer, Mannix, with no other choice, must find and deliver a member who turned informer against the dealer and his men.