Two young American missionaries, Beth and Steve, with a gospel singing background, decide to leave Texas and spread Christianity to the residents of Tressock, a small village in Scotland. Beth is a famous singer and a devout Christian, while Steve, her fiancé, supports her mission with equal enthusiasm. They choose Scotland believing the predominantly Christian nation will be receptive to their message. Upon arrival, they are welcomed and hosted by Sir Lachlan Morrison and his wife Delia, local gentry who harbor ulterior motives.

In Tressock, the couple quickly realizes that the community is engaged in pagan practices, and their own beliefs are starkly contrasted with the villagers' ancient Celtic traditions. Beth and Steve's efforts to connect with and convert the locals are met with courteous but peculiar reactions, as the townspeople have their own plans for the couple during the village's upcoming festival. Unbeknownst to them, they are being groomed for a central role in the festivities that celebrate ancient and mysterious customs.