Merlin's Wood by Robert Holdstock

A contemporary tale in which a married couple’s life is upended when an encounter with a primeval English wood awakens a lingering, seductive force tied to Arthurian legend; as myth and memory bleed into everyday reality, ancestral secrets and repressed desires resurface, driving obsession, betrayal and a tragic confrontation with a living remnant of Merlin that irrevocably alters their lives.