At the Daniel S. Totten Foundation in New York, Bertram Potts, a somber, dedicated linguistics professor, oversees the writing of an encyclopedia, on which he and his eight uniquely qualified colleagues have been toiling for nine years. When their financial backer, Miss Totten, drops by the foundation and threatens to withdraw her support, Bertram is prodded by the others to flirt with her. Charmed by Bertram's flattery, Miss Totten changes her mind, agreeing to back the encyclopedia to its completion. Soon after, a garbage man appears in the foundation's library and asks the professors for help on some radio quiz show questions. Intrigued by the garbage man's picturesque slang, Bertram declares that his section on slang is already outdated and requires further research. Bertram then takes to the streets, where he eavesdrops on a series of conversations and invites several people to participate in a slang symposium. When he invites sexy nightclub performer Sugarpuss O'Shea to attend, Sugarpuss abruptly dismisses him. Unknown to Bertram, Sugarpuss is being sought by the district attorney in connection with a murder that her gangster boyfriend, Joe Lilac, is suspected of committing, and she and Joe's henchmen, Asthma Anderson and Duke Pastrami, flee the club one step ahead of a subpoena. With no safe place to hide, Sugarpuss decides to take Bertram up on his invitation and shows up at the foundation later that night. Although pleased to see the still scantily clad Sugarpuss, Bertram, whom Sugarpuss calls "Pottsie," refuses to allow her to stay the night, but is overruled by his sex-starved colleagues. At the district attorney's office, meanwhile, Joe is confronted about a monogrammed bathrobe found in the murdered man's suitcase, which the district attorney suspects once belonged to Joe and was given to him by Sugarpuss. Concerned that Sugarpuss might be compelled to testify against Joe, his lawyer advises him to marry her. Three days later, Sugarpuss, who has been helping Bertram dissect a long list of slang expressions as well as teaching the other professors the conga, is visited by Asthma and Pastrami. The thugs present her with a pricey diamond engagement ring from Joe, and eager to become the wealthy Mrs. Lilac, Sugarpuss accepts the ring and agrees to stay at the foundation until she can safely meet Joe. Just then, however, Miss Bragg, the professors' prim housekeeper, demands that Sugarpuss leave, as she has become too much of a disruption. When Bertram asks Sugarpuss to go, admitting that her feminine ways have distracted him from his work, Sugarpuss declares that she is "just plain wacky" for him and kisses him. Bertram is so taken with Sugarpuss' kisses that he decides to propose to her, and the next morning, he gives her a small diamond engagement ring. Bertram's ardor saddens and confuses Sugarpuss, but before she can respond, Joe telephones from New Jersey. As Joe has identified himself as "Daddy," Bertram assumes he is Sugarpuss' father and asks him for permission to marry. Joe, seeing an opportunity to get Sugarpuss past the police's dragnet, goes along with the misconception and requests that the wedding be performed in New Jersey. Before the wedding party departs, however, Miss Bragg, having seen Sugarpuss' photo in the newspaper, threatens to call the police on her. After Sugarpuss slugs Miss Bragg and locks her in a closet, Bertram and the other unsuspecting professors excitedly depart for New Jersey. On the way, Professor Gurkakoff, who is driving, crashes into a signpost, disabling the car. The wedding party is forced to spend the night at an auto court, but when Sugarpuss calls Joe with the news, he insists on picking her up that night. While she waits in her bungalow, Professor Oddly, a widowed botanist, tells Bertram about his genteel honeymoon, then retires for the night. Perturbed by Oddly's remarks, Bertram seeks him out for clarification, but accidentally ends up in Sugarpuss' darkened bungalow. Believing that he is speaking to Oddly, Bertram describes his deeply felt passion for Sugarpuss, and moved by his words, she reveals herself and kisses him. At that moment, however, Joe and his gang arrive and expose Sugarpuss' deception. Finding lipstick on Bertram's face, Joe then pummels the hapless professor. After directing Miss Bragg, who escaped from the closet, and the police away from the auto court, Bertram confronts Sugarpuss. She tearfully apologizes, but Bertram returns to New York, angry and humiliated. Later, at the foundation, Oddly reveals that Sugarpuss gave him a ring to deliver to Bertram, not his, but Joe's. Bertram is buoyed by the professors' deduction that the singer is in love with him, and is unshaken when a scandalized Miss Totten arrives to announce their termination. Asthma and Pastrami then appear and, while holding the professors and Miss Totten at gunpoint, tell Sugarpuss over the phone that they are going to open fire unless she marries Joe. To protect the professors, Sugarpuss proceeds with the ceremony, which is being conducted in New Jersey by an addled-brain justice of the peace. Sugarpuss' fate appears sealed until the professors cause a heavy portrait to fall on Pastrami and then take Asthma by surprise. With help from the garbage man, the professors tickle Pastrami into revealing Sugarpuss' location and race to New Jersey, arriving seconds before she is officially wed. After Bertram beats up Joe and delivers the gangsters to the police, he convinces Sugarpuss she is worthy of him by giving her a passionate, "yum-yum" kiss.