The Ivory Dagger - Miss Silver #18.
The Ivory Dagger first published in 1951.
When Lila Dryden discovered standing over the dead body of her irritating fiance with a dagger in her hand, Miss Silver called in to investigate. What her patience and particular genius uncover Lila's talent for sleepwalking, the return of her former lover, and the victim's entire staff and circle of acquaintances - all of whom occasionally wished him dead.
Patricia Wentworth - born Dora Amy Elles - a British crime fiction writer.
She wrote a series of 32 classic-style whodunnits featuring Miss Silver. The first of which published in 1928, and the last in 1961, the year of her death.
Miss Silver, a retired governess-turned private detective, sometimes compared to Jane Marple, the elderly detective created by Agatha Christie. She works closely with Scotland Yard, especially Inspector Frank Abbott and is fond of quoting the poet Tennyson.
Miss Silver well known in the better circles of society, and she finds entree to the troubled households of the upper classes with little difficulty. In most of Miss Silver's cases there is a young couple whose romance seems ill fated because of the murder to be solved, but in Miss Silver's competent hands the case is solved, the young couple are exonerated, and all is right in this very traditional world.
Wentworth also wrote 34 books outside of that series. Her novels were the topic of Jariel D. O'Neil's 1988 doctoral dissertation.