In New York City, Max Thursday (Zachary Scott) , an alcoholic and down-and-out former police officer, works as a house detective in the run-down residence hotel of Smitty (Mary Boland). One day, Georgia Thursday (Faye Emerson), Max's ex-wife, arrives at the hotel and tells him that their son Jeff has been kidnapped. She also tells him that Jeff was last seen with her brother, Fred Mace (Dennis Patrick), who has also disappeared. When Max asks her why she has not yet notified the police, she tells him that she has been threatened with harm by Dr. Elder (Jed Prouty), her brother's disreputable associate, if she reports the crime. Max quickly sobers up and pays a visit to Elder, who greets him at gunpoint. After drugging Max, Elder knocks him unconscious and throws him into the street. Max regains consciousness in a jail cell, where he learns that Elder has been murdered and that he is being held as a suspect in the crime. Captain Tonetti (Sam Levene), head of the homicide bureau and an old friend of Max's, releases Max when Georgia provides an alibi for her ex-husband. Max's investigation into Elder soon reveals that the doctor was involved in a diamond smuggling operation headed by Otto Varkas (J. Edward Bromberg). Max finds Varkas at his warehouse and threatens to tell the police that Elder was one of Varkas' men unless Varkas tells him where he can find Fred. Varkas refuses to help Max, but on his way out, Max meets Angel (Kay Medford), a Varkas moll, who inadvertently reveals that Fred is being held captive by Varkas' men. Angel also tells Max that Elder was the pick-up man for a mysterious figure named St. Paul. While on his way to Varkas' hiding place, Max is shot in the arm - he sustaining a flesh wound - by two of Varkas' men. Despite his crippling injury which Georgia mends, Max manages to return to Varkas' warehouse, where he finds Varkas dead. A pack of cigarettes belonging to one of Varkas' men provides the clue that leads Max back to Smitty's hotel, where he discovers that St. Paul is none other than Smitty, who used the kidnapping of Jeff to force Fred to give her the jewels he got from Varkas. Smitty tells Max where to find Fred, who quietly tells Max what's going on including where to find a safe Jeff. Smitty tries to involve Max in her scheme after Max shoots her thug Stitch Olivera (Elliott Sullivan) dead, but realizes this is the end of the road for her in that he has gone straight. As an epilogue, Max, Georgia, and Jeff are seen reunited as a happy family.