It is the roaring 1920s in the city of Chicago. Helen Williams is an astute, but bashful upper class coloured detective. Helen obtained her position through a recommendation from her father after delaying an opportunity to attend Fisk University. Her mother spoke against Helen accepting the job. Williams assumed it because at the time, a young, refined, coloured woman being a detective was 'unladylike.' Her go to instrument is an heirloom magnifier she inherited from her hard working and well educated grandfather. Though some of her co-workers take some time to become accustomed to her quirks, she is admired for her detail, accepted and often called upon her colleagues for her insight. Williams has only heard of one other female coloured detective whom she never met. Helen is called in one night to help investigate some peculiar murders in which a field is often used and she now believes is the criminal mastermind's dumping ground. After a couple of days of discussing similar cases with her colleagues, Helen concludes that the executioner is a serial killer who also orders the killings. The interrelated illegal activities stem from an underground nightclub. Helen keeps in mind a note near a male decedent's body referring to a female being the next target. A group of criminals throw a brick into the station house to warn the officers to keep their investigations to crimes above ground. Lieutenant Henry Davidson orders the station on lockdown. This forces the detectives to focus even more on their case assignments and help Helen and Stephen build comradery. After he lifts the lockdown, Davidson partners Williams with Patterson undercover to further investigate murders at the speakeasy. Stephen introduces Helen to his sister Ruby to help her undergo her transformation. Williams now appears as a flapper with her station house brother, Stephen accompanying her. She is surrounded by the unfamiliar, jazz music, alcoholic beverages, and the wildest dance crazes. She notices a coloured woman being aggressively confronted by an uncouth and drunken white male. The woman orders the ‘cleaners’ to get rid of him after she has him beaten for his disrespect. At some point Helen concludes this woman is part of the operations, but not in charge. Helen meets Thaddeus, a handsome Englishman. They become enamoured with one another. Williams reminds herself to focus on the investigation. One night at the speakeasy, Helen is assaulted and nearly raped by a Negro male in one of the bigger rooms to the left of the main floor. His African male accomplice waits at the threshold of the room's door to make sure the job is done. She was able to maneuver and defend herself until Stephen nearly pummels him. Thaddeus sees the African man run and trips him, upon impact his skull is split on nails of floorboards. Helen runs out. Thaddeus carries her away and brings her to his flat. She is shy and cautious. The Englishman is protective of her. On another night at the speakeasy, Helen discovers a secret stairwell. It leads to the upper level where the serial killer and her cohorts regularly meet. When Davidson conducts a raid to solidify the undercover detectives' positions, Thaddeus brings her to his home again. After becoming more acquainted with one another, Thaddeus proposes. Helen accepts. Helen still endeavours to see her case completely resolves. She believes the woman who had the American man taken away is the criminal mastermind's target, the 'she' referred to in the note in the killing field. The final night Williams uses the hidden passageway to confront the perpetrators. She stands before them with her husband at her side. Who will leave alive?