Set in New York City during Prohibition, the story is narrated by Rose Baker, a prim young woman who works as a typist at a Manhattan police precinct, transcribing criminal confessions. She admires the Sergeant, a morally rigid superior she regards as a paternal figure, and has a cooler relationship with the Lieutenant Detective, a rumpled homicide investigator whose curt manner unsettles her. When the Volstead Act, the federal law enforcing Prohibition, transforms the precinct into a unit targeting speakeasies (illegal bars hidden behind ordinary storefronts), the surge in paperwork leads the Sergeant to request a fourth typist.
Odalie Lazare arrives for her interview in white gloves and an expensive blue suit, her jet-black hair in a chignon. Her husky voice charms both the Sergeant and the Lieutenant Detective. As she departs, a brooch of opals, diamonds, and black onyx falls from her lapel. Rose retrieves it but hides it in her desk drawer, suspecting the drop was deliberate. She acknowledges she is now bound to Odalie by temptation and shame.
Rose lives in a Brooklyn boarding house, sharing a room with Helen, a vain shopgirl who patronizes her. Rose grew up at an orphanage, where she formed a close bond with a young novice named Adele. When Rose overhears Helen and the landlady gossiping that this friendship was improper, based on a letter the landlady steamed open, Rose confronts Helen and slaps her across the face with a pair of gloves. The incident deepens her desire to leave.
On her first day at the precinct, Odalie charms the entire office. Rose begins keeping a journal of Odalie's activities. Their friendship develops quickly: Caught in a downpour, Odalie brings Rose to her luxurious hotel apartment, where she reveals that her "father" pays the rent and asks Rose to keep the arrangement secret. She proposes that Rose move in, paying the same rent she paid at the boarding house. Rose agrees and enters a world of luxury she has never known.
Odalie leads Rose through a wig shop that fronts for a speakeasy run by Gib (Harry Gibson), a tall man Odalie describes as her fiancé. Rose drinks, dances, and smokes for the first time. Odalie warns her never to tell the Sergeant, subtly threatening her housing. Rose reflects that her devotion to rules has been supplanted by her devotion to Odalie. She reveals for the first time that she is recounting these events to a doctor, indicating the narrative is told retrospectively from an institution.
The precinct is consumed by the case of Edgar Vitalli, a charming suspected serial killer whose five wives all drowned in bathtubs; Vitalli twice won acquittal by representing himself and charming juries. When a sixth victim is found and Vitalli again refuses to confess, Odalie suggests Rose type the confession herself. Rose does so, inventing incriminating details. The Sergeant reads the fabrication, comprehends what Rose has done, and after a long silence accepts it, telling the Lieutenant Detective, "We got it right here" (172).
Gib reveals Odalie's past to Rose: She was born Odalie Mae Buford near Chicago. After her father died and her mother turned to prostitution, a wealthy Hungarian client named Istvan Czakó took young Odalie to Paris and had her educated as a refined lady. When Czakó's fortune was later lost, Odalie convinced him to invest in bootlegging. She now runs the entire operation, and her precinct job is a means of manipulating the system from within.
When the Lieutenant Detective warns Rose of an impending raid at the speakeasy, she leads him to safety through a secret passageway. After the raid, Odalie gets herself assigned to every related case and secures the release of Gib and others through sessions with the Sergeant. Later, Odalie tells Rose the diamond bracelets she wears were inherited from her late father. She clasps one around Rose's wrist, declares them "sisters," and adds that sisters keep each other's secrets.
At a Long Island estate, a young man named Teddy Tricott stares at Odalie as if trying to place her. Alone with Rose, Teddy tells the story of his cousin Warren Tricott Jr. and Warren's fiancée, a mesmerizing Newport debutante named Ginevra Morris. On the night Warren planned to present Ginevra with a diamond bracelet, their car stalled on railroad tracks and a freight train killed him. A switchman matching Gib's description corroborated Ginevra's account that the death was accidental. Crucially, Ginevra was wearing both bracelets that night; one was intended for Warren's mistress, meaning she had acquired it before his death. Ginevra vanished, and Teddy believes Odalie is Ginevra. Odalie denies it and insists they leave immediately.
Back in the city, Rose witnesses Odalie intimately touching the Sergeant in the precinct hallway and is devastated. Odalie begins sending Rose on errands for the bootlegging operation. One errand takes Rose to a factory where a chemist called Dr. Spitzer warns that his latest batch of bootleg alcohol is contaminated with potentially fatal methanol. Rose delivers the tainted bottle to Odalie, who dismisses the danger. When Teddy appears at the precinct looking for Odalie, Rose, angry about the Sergeant, gives him the speakeasy's address.
On the final night, Odalie dresses them in matching black beaded gowns, darkens Rose's hair to mimic her own bob, and has them wear the matching bracelets for the first time outside the apartment. At the speakeasy, Teddy arrives using Rose's instructions. Odalie tells Rose to escort Teddy back to the apartment. When Odalie arrives later, she sends Rose out to buy cigarettes. Rose returns to find police, a crowd, and Teddy's body on the sidewalk below the terrace. The elevator boy identifies Rose as the woman who accompanied Teddy upstairs. Odalie has vanished.
Rose learns that Odalie has told police the apartment is in Rose's name, that Rose pays the rent, and that Odalie was raised in an orphanage. Rose recognizes these as details of her own life transplanted onto Odalie's story. She also learns that Gib died the same night from methanol-laced alcohol. Overwhelmed, Rose attacks the typist in the interrogation room, believing the woman is falsifying the record, and is committed to a mental institution.
There, Dr. Miles H. Benson insists Rose is actually Ginevra Morris; the orphanage has no record of her. Dr. Spitzer, arrested for his own crimes, identifies Rose as the woman who collected the tainted bottle. In a desperate attempt to prove that typed records can be falsified, Rose confesses to fabricating Vitalli's confession. This confession leads to Vitalli's acquittal and the Sergeant's forced retirement, further destroying Rose's credibility. Throughout, Rose maintains she is Rose Baker and that Odalie orchestrated everything from the moment she dropped the brooch.
In the epilogue, the Lieutenant Detective visits Rose and gives her a small box wrapped in rose-printed paper. Inside is the starburst brooch from her desk drawer. Rose understands Odalie's message: She always knew about the theft and always held this leverage. Rose kisses the Lieutenant Detective and, while he is dazed, steals his knife. Before orderlies can intervene, she gathers her hair and cuts it off, giving herself a rough bob in imitation of Odalie. As the orderlies restrain her, she takes a drag on a cigarette and thinks: "Two can play at this game" (354).