A prayer for my son

This story is set in the English Lake District and involves a mother's attempts to rescue her small son from a sadist, in this instance a grandfather with an overweening ego and a thirst for a gratification of his sense of power. The boy's mother, his aunt, the boy himself are prey to the old man's madness, and the story gathers momentum until they are forced to escape from the setting which gives him his power. It's a skilful build-up of atmosphere and suspense.