As playboy songwriter Keith Vincent callously ends an affair with a woman he calls Dolores while at the same time working on "Nocturne," his latest composition, he is shot and killed. Although Halberson, the head of the police investigation, later rules the death a suicide because Vincent's fingerprints are on the gun and powder burns appear on his hand, homicide detective Lieutenant Joe Warne is skeptical. While inspecting the crime scene, Joe notes that Vincent was still composing his song, which he had dedicated to "Dolores," when he died and kept a gallery of photographs of his lovers on his living room wall. After Vincent's servant, Eujemio, informs Joe that Vincent referred to all of his lovers as "Dolores," Joe questions the women in the photographs one by one. When the interviews yield nothing, Joe returns to Vincent's and notices a spot on the wall where a photograph had once been. Joe tracks the missing lover through a photographic studio run by a man named Shawn and interrogates the woman, Frances Ransom, at a swank swimming pool. Although Frances, a bit movie actress, gives Joe a detailed alibi, he quickly concludes that her story is a lie. Before Joe can follow up on his suspicions, however, he is suspended from the force for his brutish interrogation techniques. Unfazed by the suspension, Joe invites Frances to the Keyboard Club, where Frances' sister, Carol Page, sings. Joe asks pianist Ned "Fingers" Ford to play "Nocturne" and watches how Frances and Carol react to the tune. While Frances is nonplussed, Carol appears disturbed, and Joe decides to follow Carol home. There Carol admits that she heard Frances playing the song and knows that she was with Vincent on the night of his death. Carol also says that Frances removed her photograph a week before Vincent's demise, shortly after he had jilted her. Despite his growing attraction to Frances, Joe returns to her apartment and bluntly asks her "how she did it." Frances denies Joe's charges and permits Torp, Finger's hulking piano pusher, to beat him. At the police hospital, Joe runs into Susan Flanders, Vincent's ex-convict housemaid, who also has been badly beaten, but is unable to extract any information out of her. Joe's worldly mother, meanwhile, discusses the case at home with a friend and, while showing the friend how Vincent could not have been forced to shoot himself, accidentally fires a blank against Joe's temple. The accident convinces Joe that the powder burns on Vincent's hand could have been left by using his hand to fire a blank into the actual wound. Armed with this information, Joe corners Frances on a movie set, but is quickly turned away. Responding to a telephone message, Joe then goes to Shawn's studio, but finds the photographer's body hanging from the ceiling. He then rushes over to Frances' apartment and arrives in time to save her from gas asphyxiation. After Joe pockets a typed suicide note that implicates Frances in both Vincent's and Shawn's death, he returns to the Keyboard Club, where he and Torp fight. The victorious Joe then accuses Carol, whom he has discovered was also having an affair with Vincent, of murder. Carol pleads innocence, but is startled when a revived Frances enters the club. Eventually, Joe forces Fingers, who is secretly married to Carol, to confess that he killed Vincent out of jealousy, murdered Shawn to silence him and tried to kill Frances because she was about to unravel their scheme. In addition, Fingers admits that Torp beat up Susan because she was blackmailing Carol. As Fingers and Joe then struggle over Fingers' gun, the police arrive and arrest Fingers. Vindicated, Frances faces a happy future with Joe.