The film opens with a sweeping view of New York City, as Producer Mark Hellinger sets the stage for a narrative distinct from the ordinary. We are quickly immersed in the lives of those working the graveyard shift, showcasing their monotonous routines. A Radio Disc Jockey is seen spinning records, questioning in voiceover whether anyone is actually listening to him. A woman diligently cleans the floors of the Roxy Theatre, muttering to herself. The scene shifts silently to an apartment window where two men are grappling with a third figure. As they plot how to dispose of the body, we learn that a murder is unfolding in this city.
Later, the murderers are shown by a dock, one expressing regret about his first kill, only to be knocked unconscious by his partner, who then tosses the body into the water. We meet Detective Lt. Dan Muldoon, portrayed by Barry Fitzgerald, who is cheerfully cooking breakfast while humming an Irish folk tune. As he goes about his duties at the police station, he uncovers the tragic news that Jean Dexter, a young model, has been found drowned in her bathtub in Manhattan. Joined by novice Detective James Halloran, played by Don Taylor, Muldoon heads to the crime scene where they begin to unearth the dark secrets surrounding Jean's life.
Questions arise about how a woman with seemingly limited means could afford her luxurious apartment and expensive jewelry. Was it an ex-lover or a burglar who took her life? Delving into her past, they encounter Philip Henderson, a man rumored to have been her romantic interest, and Frank Niles, a deceitful character posing as an Ivy League gentleman.
As Muldoon pieces together the night of the murder, he finds evidence suggesting Jean was overpowered by at least two men—one who held her still while the other silenced her with chloroform before submerging her in the bathtub. Further investigation reveals that the trinkets Jean possessed were stolen, heavily implicating Niles who had gifted her much of it.
In a tense confrontation, Muldoon and Halloran catch Niles during an attempted murder, pulling him into their investigation while pressing him for the truth behind his jewelry collection and the identity of his would-be assassin. Through meticulous sleuthing, the detectives gather evidence illuminating an extensive operation dealing with stolen jewels, leading them toward the ring's orchestrators.
The pursuit climaxes in an exhilarating chase across lower Manhattan and onto the Williamsburg Bridge, culminating in a dramatic shootout that wraps up this gritty narrative.
