After the concert, Richard Halsey, a middle-aged American professor on sabbatical, decides that the Underground will be the fastest way through the rainy London night to the station where he can get his train back to Oxford. He spends his ride with an apparently drunken man who winds up being a corpse. A man representing himself as a doctor tells Halsey to go ahead and leave and that he will report the incident to the police, but Halsey decides to make the report himself. He does so, only to discover that the body and the doctor exist, by police standards, only in his imagination. When the corpse finally turns up and the police fit the story together, Halsey finds himself in a curious mesh of circumstances implicating him as the murderer. Against a serene background of gardens, country houses, history, and architectural curiosities, terror suddenly overtakes a sober scholar who wants to be a historian and finds himself instead a fugitive from both the law and the lawless.