Spoiled heiress Ellen "Ellie" Andrews has eloped with pilot and fortune-hunter King Westley against the wishes of her extremely wealthy father, Alexander Andrews, who wants to have the marriage annulled because he knows that Westley is really interested only in Ellie's money. Jumping ship in Florida, Ellie runs away and boards a Greyhound bus to New York City to reunite with her husband. She meets fellow passenger Peter Warne, a newspaper reporter who recently lost his job. Soon, Peter recognizes her and gives her a choice. If she gives him an exclusive on her story, he will help her reunite with Westley. If not, he will tell her father where she is. Ellie agrees to help.

As they go through several adventures, Ellie loses her initial disdain for Peter and they begin to fall in love. When the bus breaks down and they begin hitchhiking, they fail to secure a ride until Ellie displays a shapely leg to Danker, the next driver. When they stop en route, Danker tries to steal their luggage but Peter chases him down and seizes his Model T. Near the end of their journey, Ellie confesses her love to Peter. The owners of the motel in which they stay notice that Peter's car is gone and then expel Ellie. Believing Peter has deserted her, Ellie telephones her father, who agrees to let her marry Westley. Meanwhile, Peter has obtained money from his editor to marry Ellie but he misses her on the road. Although Ellie has no desire to be with Westley, she believes that Peter has betrayed her for the reward money and so agrees to have a second, formal wedding with Westley.

On the wedding day, she finally reveals the whole story to her father. When Peter comes to Ellie's home, Andrews offers him the reward money, but Peter insists on being paid only his expenses, a paltry $39.60 for items that he had been forced to sell to buy gasoline. When Andrews presses Peter for an explanation of his odd behavior and demands to know if he loves her, Peter first tries to dodge the questions but then admits that he loves Ellie and storms out. Westley arrives for his wedding via an autogyro, but at the ceremony, Andrews reveals to his daughter Peter's refusal of the reward money and tells her that her car is waiting by the back gate in case she changes her mind. At the last minute, just before she says "I do", she decides not to go through with the wedding. Ellie dumps Westley at the altar, bolts for her car, and drives away as the newsreel cameras crank.

A few days later, Andrews is working at his desk when Westley calls to tell him that he will take the financial settlement and not contest the annulment. His executive assistant brings him a telegram from Peter: "What's holding up the annulment, you slowpoke? The walls of Jericho are toppling!" That is a reference to a makeshift wall made of a blanket hung over a rope that was tied across the rooms separating the beds they had slept in, in order to give them each privacy while traveling together. With the annulment in hand, Andrews sends the reply, "Let 'em topple."

The last scene has Peter's battered Model T parked in a motor court in Glen Falls, Michigan. The mom-and-pop owners talk and wonder why, on such a warm night, the newlyweds (he had seen the marriage license) wanted a clothesline, an extra blanket, and the little tin trumpet that he had gotten for them. As they look at the cabin, the toy trumpet sounds a fanfare, the blanket falls to the floor, and the lights in the cabin go out.