Tommy and Tuppence Beresford have just become the proud owners of an old house in an English village. Along with the property, they have inherited some worthless bric-a-brac, including a collection of antique books. While rustling through a copy of The Black Arrow, Tuppence comes upon a series of apparently random underlinings.

However, when she writes down the letters, they spell out a very disturbing message: M a r y - J o r d a n - d i d - n o t - d i e - n a t u r a l l y...