A woman who runs a home for struggling artists has been receiving death threats, and suspicion falls on her boarders, including a pretty young poet who is the object of Jed's affections.

Checkmate is hired to protect rodeo star Len Kobalsky from his girlfriend Marcy Lowell's brother, who disapproves of their relationship and prefers she marry someone from a wealthy family such as theirs. As it turns out, the real threat to Len is from one of his fellow rodeo riders.

Checkmate is hired to protect the life of Judge Leland McIntyre, who is conducting a series of lectures concerning a trial over which he presided eight years ago resulting in him sending a man to the gas chamber. Checkmate suspects that one of the students may be connected to the case and signed up for the course to get to him. In the course of their investigation, the judge begins to question his own conduct in the trial.

Two convicts, both former Catholic schoolboys, escape by shooting a policeman, then hole up in a monastery while Dr. Hyatt is visiting and hold the Father Abbot and Dr. Hyatt hostage. Dr. Hyatt appeals to the penitential instincts of one of the men in an effort to end the situation.

The death of powerful business magnate Arnold Brack from an apparent gun accident, and his widow's and brother's apparent lack of emotion, leaves his grieving son, Daniel, to suspect it was no accident. His father recorded all of his dealings on tape, and Daniel searches for a recording of the moment of his father's death to find out what really happened. Checkmate is hired to aid in the investigation.

Jed and Dr. Hyatt go undercover as members of a hobo community to protect a man known as Doc, acknowledged leader of the community. Years ago Doc was disinherited by his wealthy father for behaving irresponsibly with money, but now his dying father wants him back, and others in his family want him dead so they won't have to pay him an allowance. When Doc winds up inheriting the entire estate, he goes to town with it, making Checkmate's job more difficult.

Karen Vale, who served five years for acting as a courier for enemy agents, is staying at a halfway house for women run by a senator's widow, Mrs. Creighton, and faces the hostility of her fellow citizens and from protesters outside the house. Mrs. Creighton hires Checkmate to protect her. In the course of their services, the Checkmate team finds Karen's greatest threat is from her former comrades who have infiltrated the protesters and even the house itself to try and bring her back into their circle, or eliminate her.

Victor Ragar, a cellist at a music conservatory that fronts for an Eastern Bloc freedom movement of which he is the leader, is in danger of being assassinated by a compatriot who accuses him of betraying the cause. The would-be assassin, Paul Delorio, also has a personal motive- Victor ran off with Paul's wife while Paul was in prison in the old country. The conservatory's director, also a member of the movement, hires Checkmate to protect Victor.

Aging theater star Richard Gilmore is nearly killed in an apparent accident during a rehearsal. His wife, actress Beatrice Lawlor, suspects it was no accident, and consults Checkmate. A subsequent attempt on his life confirms her suspicions, but the culprit turns out to be an unlikely suspect.

John Baker, a lawyer friend of Dr. Hyatt's with a mysterious past, is threatened with disbarment. He decides he wants to die, and asks a friend to arrange for his death, then changes his mind. When his friend is found murdered, he fears his death has already been arranged, and goes to Checkmate for protection.

A widow who runs a yacht club hires the Checkmate agency to investigate an apparent attempt on the life of a married man she is having an affair with, who happens to be a member of the club.

Eddie Phillips is a gifted but troubled young art student with an anger management problem. After being informed of his father's arrest on embezzlement charges, he attacks Dr. Hyatt and is put on a year's probation. Laura Hammond, an art teacher, takes an interest in Eddie and tries to help him with his anger problem by encouraging his painting, but must take care he doesn't misunderstand their relationship.

Checkmate is called to investigate the disappearance of an employee at Venus West, a beauty farm for women. Don finds himself falling for the beauty center's manager, who is not all she seems.

Jed poses as a publicity man on a movie set to keep a close watch on suicidal actress Vicky Page, accused of trying to kill another actress who she suspects is having an affair with her boyfriend, director Ernie Chapin.

In a mostly comedic episode, Jack Benny guest stars as Jack Bowen, a beloved TV comedian much like Benny himself, who is serving as the Grand Marshal of the Pioneer Bowl Parade and football game. Also in town for the big game is the Checkmate team, and while there they end up mixing business with pleasure after Jack becomes the apparent target of a would-be assassin.

An amnesiac woman is taken home from the hospital by a man claiming to be her husband, but the woman doesn't believe that she could be his wife, and despite her memory lapse believes she has reason to fear for her life. Checkmate investigates.

Police Lieutenant Dave Harker, a friend of Don's, is bitter after being denied a promotion to Captain, and decides to frame nightclub owner and high school rival Nick Culley, whom he blames for the pass over, for murder. Harker in turn is being blackmailed by a man who knows the truth. Devlin goes undercover as a rookie cop to keep an eye on Harker.

Highly successful construction engineer Howard Gentry calls on Checkmate after an apparent attempt on his life. Checkmate suspects his identical twin brother Robert, but Howard does everything he can to dissuade them of that suspicion. His reasons for doing so lead to an intriguing conclusion.

Zoe Kamens is an artist who just wants to paint honestly by copying masterpieces, but her husband, a man of questionable ethics, has been pressuring her to make copies and pass them off as originals. He in turn is being pressured by a crooked art dealer. Zoe turns to Checkmate, but keeps changing her story because of her shifting feelings for her husband, and complicating matters is the fact that she and Don were once an item, something Don has trouble forgetting.

Sid Caesar appears as Johnny Wilder, a highly popular but guilt-ridden, somewhat neurotic San Francisco disk jockey who believes that a former rival whose own career went on the skids blames Johnny and wants to kill him. The station's owner hires Checkmate to protect Johnny- maybe from himself.

The son of a prominent businessman has been murdered in San Felipe. The town suspects Juan Moreno, a migrant worker, but the men at Checkmate think he is being railroaded. They investigate, and in the process, uncover details that are embarrassing to both the defendant and the victim's family.

Gina Burton is a photo-journalist who has pictures that prove sensitive to a prominent men's club. In an effort to fend off an intruder trying to gain possession of the pictures while she's developing them, she accidentally gets acid in her eyes, resulting in permanent blindness. Hired to provide protection, Corey also helps her cope with her blindness.

Jocko, a man whom Dr. Hyatt recommended be remanded to a psychiatric facility for treatment at his parole hearing five years earlier, still holds a grudge, believing that Hyatt wanted him confined for life as a psychopath. On his birthday, Hyatt gets a surprise visit from Jocko, who holds him at gunpoint with the intention of forcing him to concoct nitro for deadly use.

At Corey's urging, a reluctant Dr. Hyatt is staying at a lodge for some much needed rest and recreation. The lodge's handyman is plotting the death of the owner, with the help of an escaped convict. The owner's wife, who is also the handyman's ex-lover, is in on the plot, but is ambivalent. When Hyatt's suspicions are aroused, he calls the Checkmate headquarters, and Jed arrives at the lodge, posing as a guest.

Luther Gage, an egomaniacal, methodical killer whom Dr. Hyatt helped send to prison, vows revenge and conducts a plot planned to the last detail to carry it out. Checkmate employs the services of Chris Devlin, seen here for the first time, to enter the prison posing as a new inmate to figure out and thwart Gage's plan.

A fictional state governor running for re-election stages a phony assassination attempt to boost his chances for victory, and hires Checkmate, ostensibly for protection, but in reality to provide an appearance of credibility. The governor's son is vocal in opposing his father's tactics, but dutifully goes along, mindful of a future political career of his own. Meanwhile, as the campaign winds down, a real threat to the governor's life emerges from within his own campaign.