Attorney Emory Olivant invites Corey, Sills and Dr. Hyatt to a party. Once all the guests have arrived, Olivant announces that they are going to play a game—a murder game in which he will be the killer.

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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.

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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.

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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.

Story tells of a demented woman out to kill private eye Anthony George. The instrument of death, as it turned out, was, a wild stallion she stocked on her ranch. Her motive was revenge. On a previous case, the private eye had brought her lover to justice and the gas chamber.

Checkmate comes to the aid of a woman with a traumatic past when it becomes evident that someone is trying to make it appear she's mentally unstable. discrediting her eye-witness testimony at a murder trial.

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.

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.

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""Ex-convict Griff Nolan is jealous because his wife Libby earns more as a magazine editor than he does as a mechanic. More domestic strife develops when Griff becomes jealous of Libby's boss Lewis Bates --- and buys a gun."" -- TV Guide

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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.

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.

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.

Arguably the finest episode of the series, featuring guest star Peter Lorre as an ex-con criminal mastermind determined to wreak revenge on master criminologist Sebastian Cabot. An intricate series of cat and mouse moves between the two geniuses culminates in a surprise and ultimately poignant ending, befitting the episode title. This episode stresses the close friendships between the three detectives of CHECKMATE INCORPORATED as it contrasts with that of the brilliant, but soulless Lorre. Directing, writing and acting are all exemplary.

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.