Christopher "Chris" Cross (Edward G. Robinson), a meek, amateur painter and cashier for clothing retailer, J.J. Hogarth & Company, is fêted by his employer, honoring him for twenty-five years of dull, repetitive service. Hogarth presents him with a watch and kind words, then leaves getting into a car with a beautiful young blonde. Walking home through Greenwich Village, Chris muses to an associate, "I wonder what it's like to be loved by a young girl." He helps Kitty (Joan Bennett), an amoral fast-talking femme fatale, he sees apparently being attacked by a man, stunning the assailant with his umbrella. Chris is unaware that the attacker was Johnny (Dan Duryea), Kitty's brutish boyfriend, and sees her safely to her apartment building. Out of gratitude and bemusement, she accepts his offer for a cup of coffee at a nearby bar. From Chris's comments about art, Kitty believes him to be a wealthy painter, adding, "To think I took you for a cashier."
Soon, Chris becomes enamored of her because his loveless marriage is tormented by his shrewish wife Adele (Rosalind Ivan), who idolizes her former husband, a policeman drowned while trying to save a woman. After Chris confesses that he is married, Johnny convinces Kitty to pursue a relationship in order to extort money from Chris. Kitty inveigles him to rent an apartment for her, one that can also be his art studio. To finance an apartment, Chris steals $500 in insurance bonds from his wife and later $1000 from his employer. Meanwhile, Johnny unsuccessfully tries selling some of Chris's paintings, attracting the interest of art critic David Janeway (Jess Barker). Kitty is maneuvered by Johnny into pretending that she painted them, charming the critic with Chris's own descriptions of his art, and Janeway promises to represent her. Adele sees her husband's paintings in the window of a commercial art gallery as the work of "Katherine March" and accuses him of copying her work. Chris confronts Kitty, who claims she sold them because she needed the money. He is so delighted that his paintings are appreciated, albeit only under Kitty's signature, that he happily lets her become the public face of his art. She becomes a huge commercial success, although Chris never receives any of the money.
Adele's supposedly dead first husband, Higgins (Charles Kemper), suddenly appears at Chris's office to extort money from him. He explains he had not drowned but had stolen money from the purse of the suicide he tried to save. Already suspected as corrupt for taking bribes from speakeasies, he had taken the opportunity to escape his crimes and his wife. Chris let Higgins into his wife's room ostensibly so he could get the insurance money from his death but did so when she was asleep in the room, reasoning that his marriage will be invalidated when his wife sees her still-living first husband. Believing he can then marry Kitty, he goes to see her but finds her in Johnny's arms. He later confronts Kitty, but still asks her to marry him; she scoffs him of him being single and that she refuses to marry him by the way he looks. Enraged with humiliation, he murders Kitty with an ice-pick. Police come to see Chris at his job, but it is not for the murder but his earlier embezzlement. Although his boss refuses to press charges, Chris is fired. Johnny is accused, convicted, and put to death for Kitty's murder, despite his attempts to implicate Chris. At the trial, all of their deceptions work against Johnny, and Chris denies painting any of the pictures. Chris goes unpunished but Kitty is erroneously recognized as a great artist. Haunted by the murder, Chris attempts to hang himself. Although rescued, he is impoverished with no way of claiming credit for his own paintings and tormented by thoughts of Kitty and Johnny being together for eternity, loving each other.