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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The Checkmate team is in Chinatown on behalf of a colleague of Dr. Hyatt's, a Dr. James Low, who claims his Chinese wife may try to kill a man who is supposedly blackmailing her in an attempt to ingratiate himself into Chinese society. Their investigation reveals that they are being used as pawns in an elaborate web of deceit, greed, and possibly murder.

Checkmate is hired by a woman to protect her husband, Stephen Jordan, who publishes a newspaper opposed to a referendum on legalized gambling in the city of Midvale. He has been receiving death threats and, thanks to Dr. Hyatt, survived an attempt to kill him by poisoning. The culprit at first is thought to be a supporter of the referendum, but there may be something in Jordan's past that could shed light on a different motive.

In a tour-de-force performance, Don Taylor guest stars as an ex-pro football player, now fronting a cheap health club and always on the make for one big score. Wealthy thrill seekers enlist him in an elaborate conspiracy to convince his college football protege to throw the big game. The detectives at Checkmate attempt to untangle the deceptions and restore Taylor's pride.

Wealthy industrialist Frederick Haley, who has been appointed to an important position at a humanitarian foundation, asks Checkmate to find out who has been threatening his mistress, whom he plans to marry after leaving his wife.

After an attempt is made on the life of bankrupt ranch owner Harl Stoner, the Checkmate agency goes undercover at the ranch's stockholder's meeting, where a ruthless business man sets out to take the ranch and split it up for sale and profit.

When a powerful millionaire dies, his three sons suddenly start to suspect everyone as potential threats to stealing the old man's fortune, including each other. They hire the Checkmate agency to keep them alive until the reading of the will. Only there may be another threat to the fortune that comes from outside the family.

A young hotel convention hostess is being used to escort businessmen attending the convention to their rooms, and then have her picture taken with them for the purpose of blackmail. The proprietress, Mary Reed, is suspicious and asks the men from Checkmate to investigate.

The personal relationship between entertainer Johnny Kay and his singing partner Pete O'Mara has hit a sour note. Corey (Anthony George), who has been asked to keep a protective eye on them, shows up during one of their recording sessions - which angers Johnny into storming out of the studio.