Life is harsh but uncomplicated and happy for the Morgan family in their coal mining village in the Rhondda Valleys. But as the 20th century approaches, the younger generation is restless.

When a charming 12-year-old girl takes on the characteristics and voices of others, doctors say there is nothing they can do. As people begin to die, the girl's mother realizes her daughter has been possessed by the devil--and that her daughter's only possible hope lies with two priests and the ancient rite of demonic exorcism.