When her patient is murdered, a private-duty nurse investigates the crime.

On a dark, stormy night, Miss Juliet Mitchell finds her nephew, Herbert Wynne, dead in his room. When she collapses, her physician, Dr. Stewart, telephones the hospital for a nurse. On the recommendation of police inspector Tom Patten, who is investigating the death, Stewart requests nurse Ruth Adams, Patten's fiancée. Outside the Mitchell house, Ruth encounters an hysterical young woman, who demands to know what has happened, and Ruth explains that she has come to care for Juliet. Although Wynne's death appears to be a suicide, Juliet insists that it was an accident. Patten is convinced it was murder, however, because there are no powder burns on the victim. When Patten questions Arthur Glenn, Juliet's lawyer, he learns that Wynne held a life insurance policy that would not pay in case of suicide. Later that evening, Ruth is wakened by a noise and notices that Juliet has left her bed. When Juliet returns, Ruth pretends to be asleep and sees her hide a newspaper under her pillow. The next morning, Ruth overhears Juliet tell her maid Mary to burn the newspaper, but Hugo, the butler, orders her to hide it in the library. Ruth tries to recover it, but Hugo interrupts her search. When Patten arrives, he explains that Wynne could have used the newspaper to absorb the powder burns and make it appear that he died accidentally so as not to nullify his insurance policy. That night, Paula Brent, the young woman who met Ruth outside the house the night of the murder, sneaks inside and tells Ruth that she knows how Wynne died, but she refuses to say more. After the autopsy rules that Wynne's death was accidental, Patten, who does not agree with the verdict, questions Paula. She says only that Wynne was afraid he might be killed, but later a neighbor tells Patten that Paula was in love with a man named Charles Elliott. Patten now believes that Elliott killed Wynne out of jealousy. Back at the house, Florence Lentz, Glenn's secretary, is attacked when she arrives with a copy of Wynne's insurance policy. Later, Ruth is also attacked. The police find the attacker in Wynne's room, and it turns out to be Elliott, who admits that he attacked Ruth, but denies that he accosted Florence. Nevertheless, Patten arrests him. When Juliet learns about the arrest, she insists that Ruth summon Glenn as she wants to make a statement clearing Elliott. To keep her statement confidential, Glenn sends Florence and Ruth from the room. Paula appears and begs Ruth to let her search Wynne's room for something that belongs to her. The two women then return upstairs, where they find Florence searching Ruth's room. Ruth's questions are interrupted by Glenn, who asks the women to witness Juliet's statement. Stewart, concerned about Juliet's condition, asks Ruth to prepare a shot, and a short time later, Juliet dies. After investigating, Stewart determines that the bottle, which was supposed to contain amyl nitrate, actually contained arsenic. Meanwhile, Paula searches Wynne's room and finds the marriage certificate that reveals her secret marriage to Wynne. She shows it to Adams and the others and adds that Florence had also intended to marry Wynne. Elliott tells Patten that not knowing about Paula's marriage, he visited Wynne to warn him to keep away from her, but Wynne was dead when he arrived. Hugo then suggests that Patten question Florence. In response to Ruth's questions, Florence admits that she and Hugo had planned to work an insurance swindle with Wynne. She is about to tell more when someone tries to shoot her from outside the room. The gunman is revealed to be Glenn, who killed Wynne when he refused to go through with the swindle. He then had Florence switch the bottles so that Juliet's statement, which revealed the swindle, could be destroyed. Now that the mystery is solved, Patten and Ruth drive to Connecticut to get married.