by Patricia Wentworth per Open Road is $1.89. This is #11 in her Miss Silver series.
Miss Silver investigates an unhappy family whose brightest beauty has just been poisoned
Lois has always dreamed of being a Latter. The Latter brothers are both so attractive—nearly as handsome as their stately manor, Latter End. After she spoils her relationship with one brother, she succeeds with the other, winning his heart with her good looks and the sizeable fortune she had won in her first marriage. But even after they’ve wed, she never quite fits in with the family. Still, she hardly expects them to kill her.
But that’s just what the psychic Memnon warns her of: poison. She laughs it off and so does everyone else, but then, like clockwork, she is dead. The police call it murder. The weapon? Poison, of course. It is a tantalizing case, complicated by the bitterness that infests Latter End, and only the brilliant Maud Silver, once a governess, now a detective, is up to the challenge.
Re the Miss Silver series from Wikipedia:
Miss Silver is a retired governess who becomes a private detective. She works closely with Scotland Yard, especially Inspector Frank Abbott. She is fond of quoting the poet Tennyson. "Miss Silver is 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."