Mac goes on vacation in Las Vegas to meet his girlfriend, a tennis professional (the first of six "girlfriends-of-the-week" who highlighted the "McMillan" series"). While she's preparing for a banquet at a Vegas tennis tournament, she's met by a man who presents her with her stepson's prize ring ("if I had been less civilized, I would have given you his finger to go with it"). The stepson, it appears, is being held hostage for the priceless diamond necklace the tennis pro is wearing, the last of her inheritance from her late husband. Mac quickly finds that it's a scam (the stepson was holed up with his girlfriend and was tricked into giving over the ring). Before the con man responsible for the theft can be found, he's murdered with a gun belonging to the tennis pro. Now Mac must clear his girlfriend of the murder and recover the necklace.

Mac comes home from a weekend fishing trip and walks right into his own funeral. On the night he was away, his apartment was annihilated by a bomb, along with a man and a young woman. Mac stays "dead" while Enright harangues a mobster who had threatened Mac, but the mobster has an alibi for the killings. Mac and a policewoman then focus on the dead woman, a student at a community college near San Francisco. She had arranged to meet someone at Mac's apartment knowing he wouldn't be there, and had brought a burly student to serve as her bodyguard (thus his corpse was misidentified as Mac's). The young woman was researching something tied to a nearby parish church founded by Catholic missionaries in the 18th century -- but what had she uncovered?

When Mac and DiMaggio go to meet a police informant at a waterfront setting (Mac complains that DiMaggio's car is not only cramped, but "has the baldest tires I've ever seen"), the informant's car suddenly starts up and nearly runs them down before plunging into the ocean. The informant is found later slumped in the driver's seat, with an empty suitcase beside him. It looks like he died from the impact, but Mac isn't sure and orders an investigation. Meanwhile, a suave "businessman" named Phillip shows up and starts following Mac around, inviting him and his girlfriend to dinner and gradually insinuating himself into their lives to the point where he becomes a stalker. Police records indicate that Phillip is a hired killer who's never been arrested, because he uses extremely creative ways to kill and set up alibis for himself. Phillip soon confirms that Mac is his target. Mac can do nothing to arrest him and gets increasingly agitated, which is just what Phillip wants -- he plans to kill Mac "in self-defense" when Mac loses his temper one time too many. Meanwhile, Mac is still investigating the murder of the informant, getting involved in a nasty real-estate dispute, and trying to find out who hired Phillip.

When Mac is scheduled to take a first-class flight from San Francisco to Hawaii, an airline executive arrives early and in mechanic's garb on the pretext of inspecting the aircraft. His real mission is to poison his wife, via cyanide injected into a champagne bottle. But a drunken passenger clamoring for more gets the lethal dose by mistake. The plane develops serious engine trouble and turns back to Los Angeles. The executive goes up to the VIP lounge to await justice -- but it comes sooner than expected when someone follows him upstairs and stabs him. Mac and a flight attendant team to try to find the killer, who may well be a member of the flight crew.

To fend off a nagging Assistant District Attorney, Mac invites her to his weekly poker game. Among the other participants is Mac's dentist, who consoles Mac for biting himself while his mouth was numb from recent work on a tooth. When the dentist leaves the poker game and goes home, he finds a local TV-news anchor dead on his couch, apparently from a heart attack. The dentist's wife (who was the TV news anchor's lover) and her father (the dentist's boss) are frantic, so the dentist loads the dead man into his own car and drives it to a culvert, crashing it so it looks like the news anchor had a heart attack while driving. But it wasn't a heart attack ... the man was poisoned by digitalis, which caused his heart to race out of control and conk out. Who gave him the digitalis, why ... and how?

The intrepid Mac is presented with a 70's version of the 1944 film noir "Laura" in his final episode. The play on names of the two detectives: McPherson and McMillan is the most clever part of this finale.