The Benevent Treasure - Miss Silver #26.
The Benevent Treasure first published in 1953.
An intriguing mystery involving an ancient British country home, a long-missing aide to two little old ladies, and their legendary treasure. Spoiler alert: the treasure is found, but not before tragedy strikes again.
Invited to live with her two great-aunts, the Misses Cara and Olivia Benevent, Candida Sayle has no home of her own and accepts. But the offer takes on an eerie quality when the aunts recall the family legacy--the Benevent Treasure that brings death to all who touch it. When Candida becomes reacquainted with local architect Stephen Eversley, he worries for her safety and calls in Miss Silver. But she is already on the case, investigating the mysterious disappearance years earlier of a man sho worked for the sisters, and knew a bit too much, perhaps, about the Benevent Treasure.
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.
Wentworth also wrote 34 books outside of that series. Her novels were the topic of Jariel D. O'Neil's 1988 doctoral dissertation.