Northern Ireland, 1960: Father Thomas Riley and Father John Thornton are dispatched by the Vatican to investigate reports of a miracle, a statue of the Virgin Mary weeping blood, at a remote Catholic asylum for immoral women. Armed with 16mm film cameras to record their findings, the priests instead discover a depraved horror show of sadistic nuns, satanism and demonic possession. Supernatural forces are at work here, but they are not the doing of God.