For mounted policeman Madoc Rhys and his wife, Janet, the pains of traveling with an infant are worth taking young Dorothy to Wales for Great-Uncle Sir Caradoc’s ninetieth birthday. Along with every other member of the Rhys clan, they make the pilgrimage to the ancestral pile, to enjoy a few days of drinks, dinner, and—as it turns out—demonic sacrifices.

On their first morning at the family manor, Madoc stumbles upon a concussed shepherd and a dismembered ram. It appears to be a botched attempt at an ancient rite, executed by one of those Welshmen who still carry a torch for the religion of the druids. For a spot of fun, the Rhys family decides to stage its own ritual—recreating the fertility ceremony of the Beltane bonfires. But when the flames turn a member of his family into a fireball, Madoc springs to action. Even five thousand miles from Canada, a Mountie always gets his man.