One night at 10:30 in a typical, cosmopolitan city, Janet Bradley goes to the apartment of Walter Bard, a private investigator who specializes in blackmail. Bard holds letters that would be damaging to someone close to Janet, and when he laughs at her admission that she could not raise enough money to get them back, she steals his gun and takes the evidence by force. As she leaves, she throws the revolver into Bard's car. Up the street, meanwhile, cynical reporter Ames introduces cub reporter Johnny Williams to the policemen at the station house. Ames tells Johnny that Lt. Sam Carson is a good, fair officer, then introduces him to the other reporters. While the men talk, they see Bard's car roll up in front of the station house, and his dead body is found inside. Ames smells a big story, as Bard was also involved in politics, and wonders if his murder was an attempt to discredit the current, corrupt city administration. When Carson finds Janet's name in Bard's appointment book, she is brought in for questioning, and he is instantly attracted to her. Janet is the daughter of Luther Bradley, the reform candidate for mayor, and so Dr. G. F. Yager, the police coroner, notifies Bradley's political rival, newspaper publisher Max Calvert, about her apparent involvement in the case. Despite Sam's hunch that Janet is innocent, Calvert pressures him to arrest her in the hope that it will ruin Bradley's chances in the upcoming election. Calvert promises Sam a promotion, but Sam insists on investigating fully before booking Janet. It is quickly proven that Janet was in Bard's apartment, and she tells Carson why she was there, although she will not reveal why Bard was blackmailing her. Meanwhile, Yager informs Calvert that Bard was killed by poison rather than the gunshot wound that they had assumed was the cause of death, and Calvert orders Yager to dispose of the body before Sam can examine it. Their plans go awry, however, when escaping inmate Zachary hides the corpse in the pressroom coat closet and takes its place in the morgue ambulance. Johnny finds the body and phones in his first scoop, after which Sam examines the corpse and realizes that something is amiss. He calls for another autopsy, which confirms that Bard died from poisoning. Sam has also been questioning Nora, Bard's estranged wife, and her lawyer and fiancé, Arthur Templeton. Although Nora and Arthur originally denied any involvement, they return to the station house to confess that they were in Bard's apartment. Nora reveals that she had gone to ask Bard for a divorce and was hiding in the bedroom when he was confronted by Janet. When she re-entered the living room after Janet left, she saw Bard die after he took a sip of his drink. Nora's flight from the apartment was seen by Arthur, who, afraid that she would be arrested for the murder, placed Bard's body in his car, shot him and then sent the car rolling toward the police station. Although Nora and Arthur are cleared, Janet remains a suspect, and Calvert Max now threatens to have Sam demoted if he does not arrest her. As he again examines Bard's effects, Sam realizes that he must have seen Flossie, an eccentric flower seller, before his death. Flossie reveals that she saw Yager enter Bard's apartment when he was not home. Sam then questions Yager, whom Bard was investigating for malpractice, and the desperate Yager attempts to escape. He is stopped by Zachary, who is returning to his jail cell, and soon confesses his guilt. At the prompting of his sergeant, Sam then asks Janet out for breakfast after informing her that she has been cleared of all suspicion.
