Wealthy, skeptical Hugh Paston, shocked by the death of his wife with her lover in a car crash, finds himself at a crossroads in his life. In search of distraction, he wanders into the shop of an antiquarian bookseller who befriends him and sparks his interest in occult literature. Hugh Paston is draw to study the Eleusinian Mysteries and, determined to evoke Pan, the goat-foot god, he buys Monks Farm, a former monastery, long unused and sinking into ruin. With the aid of Mona Wilton, a young artist, Hugh Paston refurbishes and revitalizes Monks Farm in preparation for the rites. In the ancient monastery, he is possessed by the spirit of a 15th-century prior, Ambrosius, who had been walled up in the cellar for practicing certain pagan rituals he had discovered in old Greek manuscripts in the monastery library - rituals dedicated to Pan.