After his son is murdered, Barnaby Jones comes out of retirement to find his son's killer. His son had phoned fellow detective, Frank Cannon minutes before he was murdered and so Cannon insists on helping Barnaby solve the case.
All of the clues lead them to Terry McCormack who was a client of Hal's (Barnaby son) and is being blackmailed. McCormack is running for political office and Hal was helping him cover up a young woman who committed suicide at McCormack's home when he tried to end his affair with her.
A friend of the woman's realizes what has happened and he starts blackmailing McCormack.
As the investigation unravels it turns out that McCormack himself killed Hal because he was afraid that Hal was about to turn him in for his part in covering up the young woman's suicide.