In New York City, emotionally shallow, self-absorbed sporting goods salesman named Lenny Cantrow [Charles Grodin] finds himself in an awkward situation with his girlfriend Lila [Cybill Shepherd] when he attempts to make love to her. Lila, an earnest young woman who expects long-term emotional commitment, declares herself chaste until marriage. Stymied by her resistance, Lenny hastily weds her in a traditional Jewish ceremony and they head to Miami Beach for the honeymoon. Freed from the shackles of her abstinence, Lila becomes precocious, which sets Lenny aback. Lenny makes love to her numerous times on the way down to Miami and finds himself repulsed and disappointed with his decision to marry.
In Miami, Lenny is content to go to the beach alone and soon meets Kelly Corcoran, a beautiful WASP college student on holiday with her wealthy parents. When Lila is severely sunburned, Lenny quarantines her to their hotel room while he engineers a string of contrived shenanigans to rendezvous with Kelly, fabricating stories to explain his disappearances. Lenny tells Kelly that she is the woman he has been waiting for all his life, and that he just timed it wrong. Over three days, Lenny meets secretly with Kelly and ingratiates himself into her family vacation, much to the anger of Kelly's father. To add to the absurdity, Lenny lays his cards on the table to Kelly's parents, explaining his awkward situation and impulsively committing to ending his short-lived marriage to Lila and following Kelly back to the Midwest. Meanwhile, the youthful Kelly seems indifferent to the situation and finds herself amused by Lenny's increasingly desperate behavior.
Later, Lenny takes Lila to an upscale seafood restaurant and attempts to confess that the marriage is over and that he wants to set her free. The scene turns tragic as Lila convulses in sorrow. The momentum shifts to a divorce lawyer's office, where Lenny signs away his remaining assets to start a new life with Kelly.
The obsessive Lenny travels to Kelly's parents' home in Minnesota, where he discovers two things: first, he still must win over the protective father, and second, Kelly is dating a college football star. Undeterred, he talks to Kelly alone in his car, where she admits she didn’t take him seriously in Miami but did find him attractive. Ignorant of the trouble his pursuit has caused, Kelly agrees to let Lenny continue his courtship, yet her father remains a hurdle. As Kelly and her mother begin to warm to Lenny's stubborn but earnest resolve, the father tries to lay down a bribe of $25,000—an offer Lenny refuses. In the end, they marry in a Christian church, and at the reception, Lenny flits from dull business chit-chat to listening to family members debate typical ventures, only to find himself once again out of sync with lasting commitment. He ends the night by quietly humming the tune he and Lila sang on the way to Miami, a subtle sign that the pattern may repeat itself once more.