The movie starts off with a little girl running through a village, going to get water from a nearby waterhole. There is a voiceover of a woman (Valerie), saying that the woods are dangerous, and her mother always told her to come right back after drawing water. At this point, the scene shows the girl (getting distracted) and following a boy to hunt a rabbit. They successfully catch the rabbit. Just as they are deciding over who to kill it, the scene cuts.
10 years later...
Valerie (Amanda Seyfried) is now a grown woman. She sneaks up on her boyfriend Peter (Shiloh Fernandez), who is a woodcutter, like Valerie's dad. Valerie's mother Suzette has arranged for Valerie to marry Henry, son of a rich blacksmith, which Valerie is not too happy about as she loves Peter. Just as the duo are planning to run away, a bell sounds, indicating that a creature, a wolf, feared by the villagers, has attacked a villager.
Valerie rushes back to the village. There, she is shocked to discover that it has actually been her sister, Lucy, that has been killed. Everyone is stricken with grief. It is revealed that Lucy actually was in love with Henry and upon discovering that Valerie was engaged to Henry, was grief stricken and went into the dangerous woods and got attacked by the wolf. The men of the village plan to hunt the wolf down and kill it. Meanwhile, Valerie goes to her grandmother's house, and the old lady gives Valerie a red cloak.
Henry, his father, Peter and a few other men head to the cave. Henry and his father are separated from Peter. Unexpectedly, a wolf lunges at them, killing Henry's father. However, the rest of the men manage to kill the wolf and behead him.
All is joyous, for the villagers think they have killed the wolf. However, Valerie walks past her mother, Suzette, who is embalming Henry's father, whom she had once loved. She tells Valerie that she had an affair with Henry's father before Valerie was born, resulting in the birth of Lucy.
Hence, Henry is actually Lucy's half brother and thus, Suzette cannot offer Lucy to Henry as a wife, but must offer Valerie. However, Valerie's father who is Lucy's stepfather really, still thinks Lucy is his real daughter.
Valerie has a friend who has an autistic brother. (Important fact)
There is the arrival of Father Solomon (Gary Oldman), who is some sort of expert on werewolves and the like. He tells the villagers that the wolf they have just killed is not a werewolf. The real werewolf is still out there, ready to strike again. This is because a werewolf when killed will go back to its human form. This is illustrated by a recount of how Solomon discovered that his wife was a werewolf, and he killed her. Anyway, the entire village is barricaded as anyone of them could be the werewolf. The villagers decide to celebrate anyway.
During the course of the celebrations, Valerie meets up with Peter, and they have a passionate makeout session witnessed by Henry, who realises that Valerie does not love him.
The celebration is brought to a brutal end when the real werewolf, a black scary thing, appears and goes on a killing rampage. The thing about the werewolf is that it can be killed with silver objects and cannot enter holy ground. If a person is bitten on a night of a red moon, he too will become a werewolf. Thus, the church is a safe refuge. Although it manages to kill many. Valerie and her friend are running away when the werewolf ambushes her. She notices that it has very brown eyes. However, instead of killing her, it speaks to her in growls, which she understands, but her friend doesn't. Just then Solomon comes, and the werewolf runs away. Valerie begs her friend not to tell anyone that she can speak with the wolf, for fear that the villagers will think that she is a witch.
The next morning, Solomon finds the autistic brother in a barn, in a frantic state of panic after the werewolf massacre. What is characterised as autistic behaviour is misinterpreted by Solomon to be signs that the brother is in cahoots with the werewolf. Worse still, Solomon had witnessed the brother perform a card trick and believed him to be using black magic. They capture him.
Valerie goes back to the house and watches her grandmother (her father, Cesaire's mother) tending over Suzette, who got scratched by the wolf. She notices that Grandmother too has very brown eyes, leading her to think that she is the werewolf. However, nothing happens.
Just then, Valerie's friend, who is desperately wanting to get her brother back from Solomon, goes to him to exchange money for her brother's safe return. She even offers her body, but is rejected. Finally, she brings up the information about Valerie being a witch (Valerie talked to the wolf) as a bargaining tool. She notices that he has silver fingernails, to kill werewolves. Valerie is arrested and imprisoned.
She is placed outside as a sacrifice for the wolf. But Henry and Peter rescue her. However, Peter is captured by the guards while Henry is shot. All of a sudden, the wolf appears, and Valerie rushes to the church as the werewolf cannot tread on holy ground. Solomon rushes at the wolf, and the wolf bites off his hand (the one with the silver fingernails) and it drops to the floor. Valerie manages to get to the church and the wolf follows after, but its paw touches the front step of the church and is burnt. (holy ground, remember?) The werewolf recoils and runs away. Valerie gets thrown about, and she is knocked out.
She wakes to find herself at home. She has had a horrific dream, but it makes her realise that Grandmother is the wolf. (she is wrong). She rushes to the church and picks up Solomon's hand, which had fallen to the floor, and puts it into her basket. She heads for the woods to her grandmother's house. Along the way, she encounters Henry, whom she notices has a glove on. She assumes that it is to cover up a burn and that he must be the wolf. She stabs him and flees for her grandmother's house.
On reaching there, she realises that there is her grandmother's silhouette. It speaks to her. The curtain pushes sideways to reveal a man - Valerie's father. He has a burnt hand from where he touched the holy ground while in wolf form. Valerie's father is the werewolf. He has killed Grandmother.
He explains to Valerie that all along, he had been managing to control himself from killing. He realised that the werewolf gene is passed to his eldest daughter (by lore). So he approaches Lucy in wolf form. However, Lucy is not his real daughter; hence she cannot hear him speak. This causes him to realise that his wife had an affair with Henry's father and he kills Lucy, in a fit of rage. Now he wants Valerie to be bitten so that she can become an even stronger werewolf as she is his real daughter, as well as run away with him. She tells him that she is not a killer, but he reminds her that she killed the rabbit she was hunting at the start of the story.
Just then, Peter arrives and attacks her father. In a struggle, he gets bitten (It is a red moon). However, Valerie manages to stab him with the hand with the silver fingernails and her father dies.
However, Peter has been bitten. He is going to turn into a werewolf. But first, they dispose of the body of Valerie's father. Then, Peter leaves for a remote area to control his werewolf transformation and Valerie says she'll wait for him.
Valerie continues to live in her dead grandmother's house. And one day, a werewolf approaches her house, but she knows it is Peter and smiles.