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.

A girl shows up at Corey's apartment, claiming that she is running from someone who is trying to kill her. However, the detectives all find that nothing she has said checks out, including her numerous aliases, and that she's actually an heiress running from a controlling grandmother. But it does appear that the part about someone trying to kill her may be the truth.

Barbara Rush plays a dual role in The dark divide. Why should Margaret Russell's life be threatened? Her aunt keeps getting phone calls from a woman named Nikki Garnett, threatening Margaret. What motive could the woman have?

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.

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.

A woman believes her husband has killed her male friend, who can not be found. She hires Checkmate to investigate.

Lola Tuscany, a temperamental lady soprano, is having premonitions of her death. After her concert she is almost poisoned and Checkmate Inc. is hired to keep her safe. Don Corey is skeptical, believing it is a publicity stunt, until he is nearly killed when a bomb explodes in the car he and Lola are driving in.

After two attempts on his life, big game hunter Lee Tabor brings Dr. Hyatt and Carl to his home in the Malayan jungle. He asks for their help in finding out which of his three house guests is trying to kill him.

""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

Eve Arden, plays a fashion designer, worried that someone is out to destroy her and her business. Checkmate have two main suspects.