Catherine (Keri Arnold) is a fearless eleven year old who thinks nothing of skipping school to play on the wild Yorkshire moors near her family farm. Her parents hardly notice, as they are too preoccupied by her younger brother Matthew's (Jason Walton) illness. As Matthew's condition starts to deteriorate, Catherine makes friends with Uma (Kavita Sungha), a new girl in the valley. While playing truant on the moor one day the two girls have a mysterious experience that convinces Catherine that she is the key to saving Matthew's life. To her anxious parents, Tom (Stephen Dillane) and Sue (Kerry Fox), Catherine's insistence appears to be just the petulance of a neglected child and they become angry that Catherine is giving Matthew false hope. But as a change of events unfolds which gives credibility to her story, Matthew, their Mother and the whole village begin to believe in the strength of this lonely girl's conviction.