A missionary arrives from the east and contacts Checkmate to warn them about a plot to kill Tom Lin, a Chinese patriot currently in hiding in San Francisco; he has apparently been shot in the arm while trying to find Lin and warn him of the danger he is in. It soon turns out, however, that the missionary is actually an assassin sent to kill the daughter of Win Lee, a former Chinese warlord also residing in San Francisco.
Alonzo Pace Graham, freed from prison after 15 years, seeks revenge on Dr. Carl Hyatt. Graham devises an elaborate plot intended not only to kill Hyatt but ruin his reputation as well. Hyatt is implicated in a murder - a murder that never occurred.
When a judge and friend of Dr. Hyatt receives telephone calls and letters threatening his life if a man he sent to death row is e executed, Checkmate investigates the guilty man and the judge's character.
Checkmate has more than one mystery to solve when they are hired by an unknown client to protect an unknown victim from an unknown killer at Felicia Royden's remote estate. Jed and Dr. Hyatt, posing as servants for the family, are puzzled by Mrs. Royden's strange little girl, Carol, who apparently makes up wild stories for no reason, but they soon begin to think Carol may hold the key to the mystery.
The Checkmate boys have their hands full in protecting their client Danny Whitman from racketeer Frank Marsdon when Danny starts a one-man crusade against the crime king-pin and his wife. Marsdon's drunken wife, Corinne, killed two people in a car accident, and Danny, determined not to see justice thwarted by Marsdon's threats and bribes, continues to publicize the accident and subsequent trial on his television show, gaining for him the animosity of Frank Marsdon. What Checkmate doesn't know is that Danny has now become a pawn in another person's scheme against ...
The Checkmate team has big trouble when Joe Farrell and his gang of hoods take them hostage at gunpoint. Farrell wants Don Corey to bring his estranged wife Jean and some stolen money he hid in her apartment to a boat where he intends skipping the country. If Don fails, both Jed and Dr. Hyatt, held hostage in their separate homes, will be killed. Farrell can't go for Jean himself, as rival gangsters are out after him; to complicate things even more, Farrell has a traitor in his gang trying to intercept Don and Jean who are desperately trying to bring the money to the ...
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.
Audrey Meadows stars as a writer of a scandalous, best-selling novel based on an unsolved twenty-year old murder in her small town. She is writing a sequel that reveals the killer and hires Checkmate for protection when attempts are made to silence her.
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.
Joan Fontaine plays a woman who claims her husband is trying to kill her. Corey accompanied her on a cruise ship to protect her but her odd behavior raises doubts. Also onboard watching her closely is a private detective who claims to be hired by her husband,
After Dr. Hyatt labels him a "constitutional psychopathic inferior" before the parole board, "Jocko" Townsend (Hunter) receives a sentence extension of five years. When he's released, he decides to celebrate Dr. Hyatt's birthday by holding him hostage and blowing him up at the exact hour and minute of his birth. The situation becomes more complicated as first Jed and then Don drop by to visit. Hyatt has exactly one hour to analyze Jocko's dysfunction and dissuade him from carrying out his ingenious homicidal plan..