Singer Estelita Rodriguez has come from Cuba to perform at the Club Maraca, a New York nightclub owned by her uncle, Ignacio Ortega. There she is romanced against her wishes by racketeer Norman "Normie the Knife" James, who, unknown to Estelita, has forced himself into partnership with Ignacio by threatening to harm her. One evening, thinking the mobster is following her home, Estelita sets a trap of garbage cans and other objects to impede his ardor, but catches instead Stratford E. Carver, a rural Clanton College professor who has rented an apartment in her building hoping to interview New York crooks for his research on criminal behavior. When Estelita sees the dazed professor and hears bells ring, just like one of her nightclub love songs describes, she becomes instantly infatuated and decides to pursue him. By posing as his cleaning lady, who needs time off for a family event, she secretly learns more about Stratford and his research. However, as she leaves Stratford's apartment after a cleaning session, she is seen by Stratford's jealous fiance Sylvia, who is also the daughter of his boss, Dean Enwright. After learning from Stratford that Estelita is a singer at the Club Maraca, Sylvia insists that they have dinner there so she can determine if Stratford is as innocent of dallying with her as he claims to be. However, as part of her act, Estelita kisses the professor, and Sylvia huffily breaks their engagement. The next day, Stratford admits to Estelita that he is ready to give up his research and return to the college, having realized that criminals will talk only to each other. Determined to help, Estelita teaches him some mobster mannerisms she learned from watching movies, and tells Norman's thugs who hang out at the club about a new mastermind kingpin, called "The Professor," who is setting up an organization to compete with their boss. The criminals come to Stratford, and though they find his mannerisms phony, they are intrigued by his psychological insights, and soon tell him their life stories, unaware that Estelita is secretly recording them. At the club, Norman is still trying to woo Estelita with flowers and gifts, and when that fails, he tries force, but she attacks him with a hot iron. Ignacio learns of this and fearing for her, makes plans to return her to Cuba that evening. While Estelita attempts to tell Stratford goodbye, Norman shows up looking for her, and Stratford knocks him out with help from Estelita. Stratford is finally realizing his attraction for Estelita, but when they attempt to kiss, an undercover policeman who believes that they are underworld characters, arrives and hauls them off to jail. Meanwhile, hoping to restore her relationship with Stratford, Sylvia arrives with her father at Stratford's place and they are mistakenly abducted by two of Norman's thugs and taken to the club, where the dean naively explains Stratford's research to the mobsters. Meanwhile, at the police station, the lieutenant, who knows about Stratford's research, releases Estelita and Stratford. After convincing the professor of the great danger they are in, he insists that the recordings be turned over to the police so that they can be used as evidence to arrest the mobsters. Estelita and Stratford return to his apartment to gather the recordings, but the mobsters, feeling angry and betrayed, also show up. The couple escape, but are chased through cellars and over rooftops. Realizing the crooks are using yarn from her snagged, unraveling dress to trail them, Estelita leads them to the back entrance of the police station, where the police arrest the thugs as they enter the building. Meanwhile, with Ignacio's help, Sylvia and the dean outsmart their captors and call the station to have the remaining crooks picked up at the club. Because of the evidence from the recordings, the crooks look forward to a long spell in jail and Ignacio is free from his unwanted partner. Estelita and Stratford happily resume their romance, and when they kiss, even the policemen hear bells.