At the beginning of the film a priest is shown in a church studying a strange ancient book. Outside there a violent storm is raging. The church begins to collapse and the priest is impaled by the spike on top of a fallen crucifix. Later a nun is shown bearing a strange pagan amulet to the edge of the sea. As she stands on the cliff she is approached from behind by someone or something that frightens her so much that she falls to her death. The amulet she was carrying is smashed on the rocks but it's pieces are shown being recovered by someone who is not identified.20 years later a young heiress from London, Elizabeth, is traveling to a remote convent to visit her friend. She is shown on a rustic country bus that is full of strange characters.Meanwhile, a young girl in a novice nun's cassock is shown entering an underground catacomb through a crack in a wall. She watches a sinister ritual where nun's beat themselves with whips and lay face down on the ground in some sort of pattern. The girl is then attacked from behind by someone with a knife. While the ritual continues below the girl is repeatedly stabbed. Her blood flows into a stream which pours out over a large crucifix.Elizabeth arrives at her destination during a heavy rainstorm (which continues through much of the movie) and has to deal with various creepy or insane locals before she finds someone willing to take her on a boat to the island where the convent is located. Elizabeth is greeted by the nuns and taken to the ancient Mother Superior who is blind and communicates through an assistant. She tells the Mother Superior that she is there to see why her father donated money to the convent and if she is willing to continue the charity.She is provided with a room but all her possessions are confiscated until she decides to leave. Shortly after she is befriended by a seemingly innocent novice, Sarah, who is appointed to act as her guide during her stay. Sarah tells her that the friend she came to visit has left the convent and returned to London. Elizabeth reveals to Sarah that she was actually born on the island and lived there until she was seven.Elizabeth and Sarah visit the decaying library of the convent. There they discover an ancient book with sinister images of a demonic creature. They also find a strange painting that features a pair of young girls and a pagan amulet. While Sarah is out of the room looking for more light Elizabeth is attacked by one of the nuns. Elizabeth narrowly escapes when the nun accidentally falls to her death out of an open window.Elizabeth then discovers an entrance into a labyrinth of catacombs beneath the convent. There she spies on a strange procession of nuns carrying burning crosses and a bloody corpse wrapped in a sheet. While following this procession Elizabeth gets lost and wanders into a pit-like room where a blind painter has covered the walls and canvases with enigmatic images. She recognizes one of the faces on the wall as that of her missing friend and realizes that the body the nuns were carrying might well have been hers.The next day she sees a boat leaving the island despite Sarah having told her that there would be way to reach the mainland for several days.Elizabeth begins to suspect that Sarah might not be as friendly as she appears. She also starts having strange dreams/visions. One involves seeing a crucified nun accompanied by two small girls. Later, she finds the beach covered by thousands of dead fish... she begins eating one before coming to her senses and vomiting. While wandering on the beach one of the villagers shows Elizabeth some photos of her childhood on the island which include another little girl and what seems to be Elizabeth's mother, who had supposedly died in childbirth. Elizabeth goes to her childhood home and questions the old woman who cared for her as a child. Their meeting is interrupted by the nuns when they set fire to the house. Elizabeth escapes but the old woman is hideously burned. Meanwhile Sarah is shown uncovering a piece of the shattered pagan amulet shown in the painting. A nun comes up to stab her but is later shown cut to ribbons and nailed to a chair. The blind painter gives a painting of Elizabeth to the Mother Superior. The old blind woman begins to smudge off the wet paint and reveals a demonic face underneath.Elizabeth makes her way back to the convent. There are dead and dying nuns everywhere. She is attacked by a nun wielding a huge knife but she manages to kill her by bashing her head on the stone floor. Elizabeth descends into the catacombs where she finds more dead nuns. The blind painter is shown using the Mother Superior's blood to paint more strange images on the wall. Elizabeth is then approached by Sarah, who removes the top of her cassock to reveal that much of her body is not human at all. She is not entirely human.It is revealed that Sarah is Elizabeth's sister but that she more closely resembles their mother. Their mother is actually the demon depicted in the book and on the pagan amulet. The nuns were trying to prevent Elizabeth from realizing her heritage and attempting to free her demon-mother from the walled up crypt she is trapped in. The two women had previously tried to free their demon-mother when they were children but Elizabeth had gotten scared and ran away. She and her father fled the island but it is presumed Sarah has been there ever since, waiting for her to return and complete the ceremony.Now the grown-up Sarah and Elizabeth begin the ritual again. The pieces of the shattered amulet are placed on the ground by a captured nun. Elizabeth eviscerates the nun and the falling blood causes the broken amulet to become whole again. The women raise the blood-soaked amulet and their demon-mother begins to break free of her prison.Just like before Elizabeth becomes terrified and throws the amulet... shattering it into pieces again. Sarah goes to the demon-mother while Elizabeth runs away.At the end of the movie Elizabeth is shown on the beach of the island. She is now in a nun's habit and putting on a necklace made of the center fragment of the shattered amulet. Her white eyes now look like those of the blind Mother Superior's.