«Postern of Fate» by Agatha Christie

The final Tommy & Tuppence novel.

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…