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.
A young widow is attacked and the only photograph of her dead husband, a Marine private is stolen. Checkmate investigates to thwart a conspiracy against her and the private the military claims never existed.
Barbara Rush plays a dual role as the inhibited Margaret Russell and the wild, heartless Nikki Garnett who feels no remorse for robbing a casino that results in the death of an accomplice. Checkmate is hired to prevent Nikki from destroying Margaret.
Checkmate is hired to protect an Ambassador's daughter receiving death threats from the Asian community after killing a Chinese child with her car. She has a history of speeding and is not being charged because of diplomatic immunity.
The detectives are shocked when one of their mentors, a highly respected attorney and legal scholar now terminally ill, summons them to his home, along with six other people whom he once successfully defended in murder trials. He announces that one of the six was actually guilty of the crime, though he doesn't say which one, and that he intends to make that person pay now for their crime.