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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Checkmate is an American detective television series starring Anthony George, Sebastian Cabot, and Doug McClure. The show aired on CBS Television from 1960 to 1962 for a total of 70 episodes and was produced by Jack Benny's production company, "JaMco Productions" in co-operation with Revue Studios. Guest stars included Charles Laughton, Peter Lorre, and Lee Marvin, among many other commensurately prominent performers.