Ukridge and Corky run into a friend of Ukridge's, a chauffeur driving a shiny new Daimler, and he offers to take them for a ride. Along the way they are seen by a creditor of Ukridge's, who they shake off, and almost hit a young girl, who Ukridge insists they drive to her home near Clapham Common. He befriends her family, who are impressed by the car and Ukridge's famous Aunt Julia.
When Corky meets Ukridge a week later in the British Museum, he is accompanied by two children. He reveals he has been visiting the house, mainly for the free food, and promising to take the family out on trips in his friend's car, which they believe to be his, and to introduce them to his aunt, who, he reveals, has disowned him, in a letter which states "from now on, I have no nephew".
Returning from short holiday, Corky hears from George Tupper that Ukridge is engaged. Visiting his friend, he finds him with a black eye, and hears the tale of how Ukridge found himself inadvertently engaged to the girl from Clapham Common, and got punched by a rival suitor named Fitch. As they talk on Ukridge's doorstep, the creditor from the car ride arrives, and Ukridge hides. A friendly passer-by soothes to enraged creditor, arguing that he knows where Ukridge lives; Ukridge moves out of his house, remarking on the good fortune that led him to use the peudonym "Mr. Smallweed" when dealing with the man.
Ukridge and Corky form a plot to get Ukridge out of th eengagement by feigning ill-health, but as Corky is delivering his speech to the family, the passer-by arrives. He is George Fitch, Ukridge's rival for the girl; he reveals that Ukridge is an impoverished imposter, in fact called Smallweed, and produces the creditor to prove it. He also bears a letter from Ukridge's aunt, claiming that she has no nephew. Once Corky has paid off the debt to the creditor, the two are chased from the house.