In the summer of 1976, on holiday in South Wales, fifteen-year-old Richard is shocked and fascinated to meet the tenants of the historic Wish House. Jay Dalton is a well-known artist, and his large, bohemian family - casually stripping naked on the beach, smoking dope, ignoring convention - seem astonishingly glamorous. Richard falls under the spell of beautiful, free-spirited Clio, Jay's daughter. She seduces him in a secret forest grotto, where they spend idyllic days playing out her favourite Celtic myths of brave grail knights and powerful enchantresses.
But why does Jay paint so many nudes of Clio? Why is he obsessed with the need to paint Richard? Why does his wife grow poisonous plants in her Witch's Garden? The Daltons' dark secrets draw Richard into a world of disturbing relationships, where he discovers, too late, that his innocent arrival at the Wish House was no accident . . .