After being appointed San Francisco Police Commissioner, former military officer and lawyer Stuart McMillan works on a number of challenging cases with the assistance of his wife, Sarah, whose father was employed at the Social Security Bureau.
The adventures of Mac and Sally continue, as the two attend a séance. Sally faces danger when a murderous psychopath threatens her. Criminals replace Mac with another person to help them get rid of a witness in a case they are involved in.
In season 3, Mac's family reunion in Scotland turns into a tragedy after his uncle allegedly commits suicide. Mac also pretends to be a fugitive to discover the arrival of an illegal shipment of gold.
Investigations into various incidents continue in San Francisco, as Mac's old friend is declared dead 10 years before he was actually killed. Police officers including Mac become suspects after an author is murdered on a train bound for Los Angeles.
In season 5, Mac's mother's friend's party ends in an attempted murder. Sally and Mac discover an old skeleton in their fireplace, and a member of Mildred's family becomes a suspect after the death of her wealthy aunt.
In season 6, a man tricks Mac's girlfriend into giving him her necklace and is later found killed with her weapon. Mac discovers that he was the target in the explosion of the building in which he lives, and investigations indicate that the death of a model was actually murder.