Renowned exercise guru Milo Janus (Robert Conrad) runs a chain of successful gyms. His charm is not enough to calm the anger of franchise owner Gene Stafford (Philip Bruns), who has found out how Janus overcharges his franchises for equipment and supplies, depositing the profits in offshore bank accounts. When Stafford threatens to organize other victims of Janus and to go public with a class action suit, Janus kills him. He makes it look like Stafford was working out, trying to lift weights too heavy for him, with the result being that the barbell fell and crushed his windpipe. Collin Wilcox plays Ruth Stafford (the victim's distraught and sometimes boozy ex-wife/widow, who thoroughly mistrusts Janus), Gretchen Corbett plays Janus's secretary, and Pat Harrington, Jr. plays a shifty business associate of Janus.

After years of marriage to his domineering wife, Frances (Antoinette Bower), professional photographer Paul Galesko (Dick Van Dyke) decides to kill her. He hires ex-con Alvin Deschler (Don Gordon) to rent an isolated ranch house. Galesko persuades his wife to accompany him there and she grudgingly agrees. He ties her to a chair, photographs the scene, and then shoots her. He sets things up so it will appear he is elsewhere when the pictures were taken. Galesko meets Deschler at a junkyard. After shooting Deschler with a revolver, Galesko shoots himself in the leg with the pistol used in the first murder, then plants that gun on Deschler so that it will appear the "kidnapper" was killed in self-defense. JoAnna Cameron plays Galesko's assistant, with whom he is planning a romantic getaway. Michael Strong, Larry Storch, Vito Scotti, and John Ashton guest star, as does Joyce Van Patten, playing a nun running a homeless shelter who assumes, when she meets Columbo, that he is down and out and in need of some food and a better coat.

Final clue/twist: Columbo stages a false accusation using a mirror-inverted version of the kidnapping photo Galesko used to fabricate an alibi. The reverse negative shows a different time on a clock in the photo, a time for which Galesko has no alibi. An increasingly riled Galesko accuses Columbo of framing him with false evidence, and becomes more incensed when Columbo tells him the original photo was accidentally destroyed. Galesko grabs a camera from a shelf where there are twelve other cameras, and shows Columbo a negative that is still inside it. Galesko says the negative proves him right about which way the clock is pointing in the original photograph. Galesko has thus given himself away. He had no way of knowing which camera had been used as part of the kidnapping scheme, or that the negative was still in the back of that camera. Galesko, defeated, realizes that Columbo had staged the false arrest with the exact purpose of getting him to lose his cool so he would rashly identify the camera.

The outside set of Deschler's hotel room is the set of Psycho.

Colonel Lyle C. Rumford (Patrick McGoohan), head of the Haynes Military Academy, an all-boys school, is told by the Board of Trustees president William Haynes (Tom Simcox), with whom Rumford has a contentious relationship, that due to declining enrollment it must be converted into a coed school. Haynes also makes clear that Rumford will no longer be in charge of the revamped institution. Rumford rigs a school cannon by blocking its discharge with a cleaning rag, then modifies a shell with a more powerful explosive so that the cannon will explode when Haynes fires it the next morning, at a ceremonial occasion. Rumford pins the accident on a cadet, Roy Springer (Mark Wheeler), who has a history of behavioral demerits. Eventually Rumford’s own fanatical sense of duty provides Columbo the clues that lead to Rumford’s incrimination.

Final clue/twist: Rumford, an absolute stickler for the academy’s rules, is determined to find a bottle of prohibited cider that he knows is on the premises. Columbo himself finds the cider, and realizes there is a connection between it and the murder. He gains the confidence of the cadets who made the cider, and has them tell him everything about how and when it was made. Once he learns that information, he asks Rumford if he had seen the cider previously. When Rumford says yes, it incriminates him. Columbo tells him he could have seen the cider only on the morning of the murder (the cider had been hung out to ferment at night, and as such was only visible around sunrise), and only if he was standing very near the cannon (because of the location of the trees on the academy grounds). So on the morning of the murder Rumford was not asleep, as he had claimed; instead, he must have been at the cannon.

While aboard a Mexican cruise he takes frequently, auto executive Hayden Danziger (Robert Vaughn) has been having an affair with the lounge singer Rosanna Wells (Poupée Bocar). When Wells threatens to expose their affair to Danziger's wife, Sylvia (Jane Greer), Danziger decides to get rid of Wells. To set up his alibi, he inhales some amyl nitrite to feign a heart attack in the swimming pool, so that he will be checked into the ship's hospital.

During a lapse in security, Danziger dons a crewman's uniform, sneaks out of his hospital bed, and waits in Wells's cabin for her performance break. When Wells comes back, Danziger shoots her, plants evidence to implicate a band musician, Lloyd Harrington (Dean Stockwell) – who had been in a relationship with Wells before she discarded him – ditches the pistol, and returns to the hospital before the doctors can find him missing. Columbo, vacationing on the cruise with his wife, is pressed into service by the ship's captain (Patrick Macnee). Bernard Fox and Robert Douglas also guest star.

Harold Van Wick (Oskar Werner), the controlling, arrogant, gadget-obsessed president of Midas Electronics, has wired his estate-home with closed-circuit television cameras and video recorders. His mother-in-law Margaret Midas (Martha Scott), who owns the company, and who blames a steep drop in profits on Van Wick's costly fascination with obscure gadgetry, orders him to resign his post by the following morning, or she will expose his philandering ways to his wife, her daughter, Elizabeth (Gena Rowlands). Van Wick has already set in motion a scheme to murder her. He rigs his high-tech home security system and shoots Margaret when she is in the viewing field of one camera, feeding a recording of an empty study to the guard monitoring the estate's rooms. Having already forced open a window and planted footprints outside it to make the murder look like the deed of a burglar, he then uses a timer to play back the tape of the shooting to the gatehouse guard's monitor to make it look like Margaret was shot by an intruder after Van Wick had left the house for a party. Robert Brown played Arthur Midas, Margaret's son and Elizabeth's brother. Patricia Barry plays the owner of an art gallery which provided Van Wick with his ostensible alibi, and Trisha Noble plays her sexy assistant, who may have had an affair with Van Wick.

Psychiatrist Dr. Mark Collier (George Hamilton) is having an affair with a patient of his, rich housewife Nadia Donner (Lesley Ann Warren). One day, Nadia invites Mark to a weekend sex vacation at the Donner beach house. Collier shows up at the beach house only to be unpleasantly surprised by Nadia's husband, Carl (Stephen Elliott). The two men get into a violent confrontation over Collier's affair with and drugging of Nadia, with Carl threatening to damage Collier's reputation. When Collier surprises Carl by attempting to leave with Nadia in tow, Carl attacks him. A scuffle ensues, which ends with Collier bludgeoning Carl with a fireplace poker. After telling Nadia to explain it to the police as a home invasion that turned tragic, done by several masked men, Collier drives off, almost running over a blind man walking his dog past the beach house. Investigating the scene, Columbo is not satisfied with Nadia's version of events, wondering why Nadia didn't see the headlights of the burglars' car. When Columbo tells Collier that Nadia's story is not credible, Collier secretly hypnotizes her into, in effect, committing suicide by taking a deadly dive from her fifth floor balcony into the swimming pool below.