The Shadow Key

After a grave mistake, Henry Talbot has been forced to take a position as a village doctor in remote Wales, where he can't speak the language and belief in myth and magic is rife. When Henry discovers his predecessor died in mysterious circumstances, and starts to notice a cryptic symbol appearing in odd places, he sets out to find answers. The lady of the manor, Linette Tresilian, is vexingly unhelpful at first.
She seems to know little about the shelves of occult books Henry notices in her family's library. But Linette has suspicions of her own about what's happened in the village and their investigations will bind their destinies in ways neither thought possible.