When mystery girl Perdita arrives in the small Welsh village of Pont Wan in 1959 the lives of its inhabitants, good, bad and downright evil, will never be the same again. While a few people grow to like the plucky young stranger, most remain hateful, laying all their ills at her door. Darkening the atmosphere further is the shadow of fifteenth-century witch and wisewoman, Mother Olwyn, who prophesied that the weak bridge from which the village took its name would one day fall for a third time, marking the end of the world. Judging by the poor state of the bridge, that time looks imminent.