Luke Fitzwilliam, a retired colonial policeman, has returned to England and chances to converse on a train with a woman who reminds him of a favorite aunt. She informs him that she is reporting three murders to Scotland Yard and is hoping to prevent a fourth, that of a village doctor. Before she can do so, she is killed by a car, and a short time later the doctor she mentioned is killed. Fitzwilliam decides to investigate these five deaths.

It was just Luke Fitzwilliam's luck to be stuck next to a dotty old woman like Miss Fullerton on the London-bound train—although he found himself quite entertained with her tall tales about a series of perfect murders in the quaint village of Wychwood. But when he reads the next day of the freak accident that killed her, too, Fitzwilliam's amusement turns to grave concern. A visit to the isolated village confirms his worst fears. For Wychwood seems to be divided by an eccentric lot of locals: those who are in on a dark and dangerous secret—and those who don't live long enough to share it.