"Mark's Priory," the Lebanons' family seat, is a house of terror to Ilsa Crane, Lady Lebanon's niece and secretary. The strange behavior of two sinister footmen, Gilder and Brooks, adds greatly to her fear, and her sole consolation lies in the sympathy extended her by young Lord William "Willie" Lebanon. A young architect, Richard Ferraby, arrives from London to inspect the ancient home in regards to renovations, and he and Isla are immediately attracted to each other. Lady Lebanon tells her son that he must marry Isla to carry on the family name but Lord Willie tells her he has no intentions of marrying. Later, the family physician, Dr. Amersham, arrives and it is evident he has some hold over Lady Lebanon. The chauffeur, Studd, hints that he knew Amersham in India and that Amersham was discharged from the Indian Army under unsavory circumstances. Isla and Richard find Studd murdered and suspicion falls on the gamekeeper, Tilling, whose wife had been more than a little friendly with Studd. But Chief Inspector Tanner and Deputy Sergeant Totty arrive from Scotland Yard and uncover evidence that points to Dr. Aversham as the killer, and Lord Willie substantiates the clue by telling them that Aversham had strangled a young Eurasian girl in India by using a red scarf--and Studd was found strangled with a red scarf. Just when the police are about to fold up their tidy little case, a telegram arrives from "Mark's Priory" informing them that Aversham has just been found murdered--strangled with a red scarf. Back to the drawing board.