When his mistress Karen Armsby commits suicide during a party at the home of rising young político, Terry McCormack, he persuades private eye Hal Jones to help move her body to her own apartment so he won't be implicated.
When a blackmailer phones, McCormack assumes it's Jones. He gets Jones to agree to come to the drop, and then tails him. When he sees Jones in a phone booth, McCormack kills him.
Jones had been calling his friend, Frank Cannon, for advice on the messy affair. Cannon comes over the next morning to find Hal is dead, and his father, Barnaby Jones, who'd retired and given his son the business, at the house.
When another blackmailing call comes in, McCormack realizes he got the wrong man. Barnaby calls in the course of his investigation and McCormack hires him to find the blackmailer, who he claims is Hal's killer.
Karen's escort at the party, Reed Carpenter, turns out to be the blackmailer. Jones is concealed when McCormack delivers the money and accuses him of the murder. Carpenter denies it, Jones reveals himself, and the trapped McCormack tries to kill Jones but loses his nerve. Jones decides to come out of retirement and reestablish the business he'd left his son.