Vivian Heldon, a "B-girl" at the Grass Skirt café in Boston, lives in a boardinghouse operated by Mrs. Smerrling. Desperate for rent money, Vivian telephones James Joshua Harkley, a married man with whom she had an affair, and demands that he meet her at the Grass Skirt. While waiting for Harkley, Vivian meets Henry Shanway, a drunk and despondent young man whose wife has just lost their baby in childbirth. When Harkley fails to show up, Vivian offers to drive Henry home and steals his car. She then arranges a meeting with Harkley at Lakeman's Hollow, on Cape Cod. When Vivian demands money from Harkley, he shoots her and tries to cover up the murder by sending her car into a pond. Three months later, the skeletal remains of Vivian's body are found on a Cape Cod beach. Police Lieutenant Peter Moralas and his associate, Detective Tim Sharkey, begin an investigation into the murder by visiting the Department of Legal Medicine at Harvard University. There they meet forensics expert Dr. McAdoo, who determines that the victim was a female in her mid-twenties who died sometime in late May. While searching through photographs of all the missing persons in the area, Peter and Tim discover Vivian's photograph, and realize that her facial features match the contours of the victim's skull. To learn more about Vivian's disappearance, Peter visits Mrs. Smerrling's boardinghouse, where they find items in Vivian's suitcase that clearly establish her as the murder victim. When Mrs. Smerrling learns that Vivian was murdered near Hyannis, she tracks down Harkley through a Hyannis telephone number scrawled on the wall near the hallway telephone. Mrs. Smerrling then visits Harkley and makes an unsuccessful attempt to extort money from him in exchange for her silence. Before leaving, however, Mrs. Smerrling manages to secretly steal Harkley's gun. Meanwhile, Peter visits a number of Vivian's former associates, including a bartender, a mortician and a physician. Peter later visits Henry when it is determined that he owned the car in which Vivian was last seen. Henry denies any association with Vivian, but a tattoo artist friend of Vivian's later identifies Henry as the man who escorted Vivian home from the Grass Skirt on the night she was killed. Peter charges Henry with the strangulation murder of Vivian, but complications arise in the case when McAdoo determines that Vivian died of a gunshot wound. Realizing that his case against Henry can only proceed if the pistol used to kill Vivian is found, Peter begins questioning other people who may have associated with Vivian. A check of the boardinghouse telephone bill leads Peter to Harkley, who denies having known Vivian and watches nervously as Peter searches his office. Later, Harkley visits Mrs. Smerrling, accuses her of stealing his pistol and offers her $500 in exchange for the gun. When Mrs. Smerrling demands $20,000, Harkley forces her to tell him where it is hidden and then knocks her unconscious with a candlestick. Moments later, Peter arrives at the boardinghouse and sees a man fleeing, but he is unable to catch him. A breakthrough in the case comes when Peter finds a train station baggage check receipt hidden in Mrs. Smerrling's bird cage. Peter and Tim race to the train station, and arrive in time to catch Harkley trying to flee with Mrs. Smerrling's suitcase. Harkley is then arrested and charged with Vivian's murder, and Henry is cleared of any wrongdoing.