The show is about an Inspector (later Captain) with the San Francisco Police Department's elite "Special Investigations Unit". As the show begins, he's in his 40s, twice-divorced, and dealing with a feisty teenage daughter, Cassidy. Nash convinces recently-retired Inspector Joe Dominguez to return to the force to partner with him. Nash and Joe cruise the streets of San Francisco in Nash's electric yellow 1971 Plymouth Barracuda convertible, a gift from Nash's brother Bobby just before Bobby left for the Vietnam War. Bobby Bridges was reported as MIA, but turns up in later seasons. Nash's father Nick suffers from mild dementia and has a habit of getting kicked out of nursing homes. He eventually moves in with Nash, and is often involved in comic subplots.