The Shadow Key by Susan Stokes-Chapman

There's something mysterious about the village of Penhelyg. Will unlocking its truth bring light or darkness?

Meirionydd, 1783. Henry Talbot has been dismissed from his post at a prestigious London hospital. The only job he can find is as a physician in the backwaters of Wales where he can't speak the language, belief in myth and magic is rife, and the villagers treat him with bewildering suspicion. When Henry discovers his predecessor died under mysterious circumstances, he is determined to find answers.

Linette Tresilian, the unconventional mistress of Plas Helyg, lives a lonely life. Her father is long dead, her mother haunted by demons which keep her locked away in her room, and her cousin treats her with cool disdain - she has had no choice but to become fiercely self-reliant.

Linette has always suspected something is not quite right in the village, but it is only through Henry's investigations that the truth about those closest to her will come to light...a truth that will bind hers and Henry's destinies together in ways neither thought possible.