The Twisted Root — Anne Perry

A young groom enlists private investigator William Monk to track down his fiancee, Miriam Gardiner, who disappeared suddenly from a party at a luxurious Bayswater mansion. But Monk soon finds the coach in which Miriam fled and, nearby, the murdered body of the coachman. There is no trace of Miriam. What strange compulsion could have driven the beautiful widow to abandon the prospect of a loving marriage and financial abundance? Monk and clever nurse Hester Latterly, themselves now newlyweds, desperately pursue the elusive truth--and an unknown killer whose malign brilliance they have scarcely begun to fathom....