Maleva: [narrating] Even a man who is pure in heart and says his prayers by night, may become a wolf when the wolfbane blooms, and the autumn moon is bright.
Ben: Show yourself! I know you are out there! . . . Help! . . . Help me! Somebody help me! . . . Help!
In 1891, Gwen Conliffe (Emily Blunt) searches out Lawrence Talbot (Benicio del Toro), a renowned Shakespearean actor touring London, regarding his brother, Ben.
Gwen: My name is Gwen Confliffe, and I'm engaged to your brother Ben.
Lawrence: Is Ben here?
Gwen: No. I'm afraid no one knows where Ben is, which is why I am here. . . Ben is missing from Blackmoor. He's gone.
Lawrence: Did my father send you?
Gwen: No, I'm here on my own. It's been nearly a month since anyone has seen Ben, and we knew that you were in London. I'd hope you had received some word.
Lawrence: Why do you think he is in trouble?
Gwen: Because the night he went missing, two villagers were killed. Will you help us?
Lawrence declines to help due to performance commitments.
Gwen: It must be a wonderful luxury doing battle with imaginary demons, Mr. Talbot. Mine right now are very real.
Her comment as she left, made a mark on Lawrence, so he later decides to take a train to the family's estate near Blackmoor.
During the trip, a passenger (Max Von Sydow) in his cab offers him a cane with a silver wolf's head on it. The head detaches, revealing a long dagger. Lawrence kindly refuses and takes a nap. When he awakes, the passenger is gone, but the cane is still there, so he decides to keep it. When Lawrence arrives, Talbot Hall is in disrepair. He is greeted by his father, Sir John Talbot (Anthony Hopkins), pointing a shotgun at him.
Lawrence: Hello father.
Sir John: Lo and behold, the prodigal son returns. I hope you're not expecting a fatted calf.
John tells him that Ben's mauled body had been found the day before. Lawrence goes into town to see the body, which is kept at the local slaughterhouse. The butcher gives Ben's personal effects to Lawrence. The butcher warns not to look at Ben, but Lawrence insists. He's horrified when he uncovers his brother's corpse.
Later, in the local tavern, Lawrence overhears the locals debate about who was responsible. Among Ben's belongings was a medallion that had been purchased from the gypsies. Lawrence fiddles with it while listening to the patrons, who are unaware he is Lawrence Talbot.
Montford: What if it wasn't a beast at all, but a cunning murderer? Someone who bore a grudge against one of these men. To misdirect the authorities, he kills the men, and then he tears up the bodies to make it look like a wild beast was responsible?
Constable Nye: Ridiculous! Who would go to such lengths?
Kirk: What about that gypsy dancing bear? It could have done it.
Montford: That mangy thing? Kill three men? I doubt it.
Reverend Fisk: I saw the bodies with my own eyes. Unnatural wounds. Most unnatural. Made by a fell creature I'd say.
Kirk: Damn gypsies wandering the countryside bringing their woe and deviltry with them. They show up and two weeks later this happens! My guess is Ben Talbot went to their camp to have it off with a gypsy whore. The bear gets hold of him, and they dump what's left of him in the ditch!
MacQueen: Got nothing to do with the gypsies.
Everyone turns to look at MacQueen.
MacQueen: Twenty-five years ago now, me Pa found him. Quinn Noddy and all his flock. Brains and guts and God-knows-what lying all over the moor for a quarter mile. And, Quinn, the look on his face. Like he'd been eaten alive. Whatever did it was big, had claws, and didn't mind a load of buckshot. After that me Pa went home and melted down me Ma's wedding spoons and cast silver bullets on 'em. Wouldn't leave the house on a full moon from then on.
Montford: Ha! He thought it was a werewolf.
Kirk: . . . I still say that bear's to blame.
Montford starts throwing insults about mother Talbot being a whore. This enrages Lawrence and he tries to pick a fight before he is escorted out. They finally realize who he is now.
That evening, Lawrence is in the dining room with his father at Talbot Hall. Gwen enters a moment later.
Sir John: I was telling my son a moment ago, that the telegraph system does reach us here at lonely old Black moor.
Gwen: [to Lawrence] Do you find your home much changed, Mr. Talbot?
Lawrence: Blackmoor does seem rather the same as I left it.
Sir John: How so?
Lawrence: Villagers . . . they still have the same wild ideas.
Sir John: Ignorant. Superstitious. To a worldly man such as yourself, we're savages at the end of the earth.
Gwen: I didn't intend to start a squabble.
Sir John and Lawrence continue badgering each other until Gwen finally excuses herself. Later in the den, Sir John and Lawrence discuss his mother's death among other topics. Lawrence wonders what kind of thing could have made such terrible wounds on his brother, which Sir John speculates on animal or man. Lawrence also mentions the strange medallion found in Ben's belongings.
Sir John: Yes, St. Columbanus. He was an Eastern saint. He was also a Gypsy.
Lawrence: So, did Ben have dealings with the Gypsies?
Sir John: Yes, he was our negotiator. The local gentry would pay a fee, and the Gypsies would keep their criminal activities to a minimum and they would move on once they'd sold the local lads all the wine and dark-haired ladies they could stand.
During the discussion, Sir John has been blowing out all the candles in the den to make the room dark, then turns to his telescope and recites . . .
Sir John: "That orbed maiden with white fire laden whom mortals call the Moon, glides glimmering o'er my fleece-like floor. By the midnight breezes strewn."
Sir John looks at the Moon through the telescope.
Sir John: She exerts enormous power, doesn't she?
Lawrence: I wish things were different.
Sir John: Never look back, Lawrence. Never look back. The past is a wilderness of horrors. Lawrence . . . I'm glad you're home.
Later, Lawrence pays Gwen a visit and apologizes for his behavior in the dining room.
Lawrence: These were Ben's. He'd want you to have them.
He hands her a ring and a picture of her.
Lawrence: If there is anything you need, anything at all, please let me know.
Gwen: I want to know what happened to him.
Lawrence: I'll do everything I can.
Gwen: Thank you. Thanks for coming.
Walking down a hall, he hears the voices of children. He opens the door and has flashbacks of his childhood. He's in his old bedroom shared by his brother. The flashback continues of the two waking up after hear a noise. Lawrence wanders out to the courtyard and sees his father holding his mother's body. Her throat is slit and she is holding a razor.
The next day, they attend the funeral. The full Moon is visible even by day. Ben's body is carried into the mausoleum.
Afterwards, Lawrence runs into Gwen who is resting on the ground looking at a waterfall - a favorite play area for the Lawrence brothers when they were children. He reveals to her that he has been estranged from his family for many years, since his father sent him to an insane asylum after witnessing his mother's mysterious death. Sometime later, Gwen is boarding a stagecoach.
Sir John: You sure you won't stay one more night?
Gwen: My father has lodgings at the inn, and that's more convenient for the train so . . .
She turns to Lawrence.
Gwen: When do you return to London?
Lawrence: Not till I find out what happened to my brother.
Gwen turns and climbs into the carriage. She and Lawrence exchange a brief glance before the driver pulls away.
Sir John: Lawrence, that's all well and good, but I think your inquiry could wait until tomorrow. The moon is full tonight and I'd prefer that you stay inside in the event that your raving lunatic theory is correct. I don't want to lose you too.
Ignoring his father's advice, Lawrence goes to the gypsy camp on the night of a full moon. He questions Maleva (Geraldine Chaplin) about his brother when suddenly the camp has been invaded by the local townspeople to force them to turn over a dancing bear that might have been the killer. But a superhumanly strong wolf-like creature descends on the camp, slaughtering many people.
Lawrence sees a young boy run into the woods. Intending to rescue him, Lawrence follows but is attacked by the creature, who bites him on the shoulder before being chased off by the armed townspeople. Maleva sutures his wounds. Her daughter says Lawrence should be killed, but Maleva refuses, saying he is still a man. Only a loved one can kill him.
Maleva brings the wounded Lawrence to Talbot Hall. Gwen returns to Talbot Hall to nurse Lawrence back to health. He has several fearful dreams but after a few weeks appears to have completely healed.
Lawrence pays a visit to John's faithful manservant, Singh (Art Malik), who implies that something monstrous is on the loose in Blackmoor..
Lawrence: Do you believe in curses?
Singh: This house has seen it's fair share of tragedy. Your mother. Your brother. Yes, I believe in curses.
Lawrence: [seeing the silver bullets] Singh, I didn't know you hunted monsters.
Singh: [ominously] Sometimes monsters hunt you.
Inspector Aberline (Hugo Weaving) arrives from London to investigate the recent murders. He suspects Lawrence because of his past mental issues.
Lawrence: I get your implication, and resent it. You're clearly aware of my personal history, as I believe I'm aware of yours. Weren't you in charge of the Ripper case a couple of years back?
Aberline: You're a direct man. So I'll be equally direct with you. I am not your enemy, Mr. Talbot. You've been seen as Hamlet, Macbeth, Richard III, all with that same face. A prudent man would ask who else might be living inside that head of yours?
The inspector informs him he will check up on his recent whereabouts and send in a specialist to examine his wound.
Lawrence and Gwen share a light moment for a change as he shows her how to skip rocks across the water. Suddenly he realizes he has superhuman hearing. He can his horses in the distance. A town posse has arrived and want to bring Lawrence in, knowing he now bears the mark of the beast and a full Moon is pending. Three men grab Lawrence, but struggle to contain him. Sir John shoots a statue next to Colonel Montford causing him to fall off his horse.
Montford: My eyes . . . Damn you, Talbot!
Sir John: I'm sorry, Colonel. I meant to shoot you. Sadly, I'm not quite the marksman I used to be . . . I must be getting old.
Sir John threatens to shoot them for trespassing and claims Singh is on top of the mansion with a reloading rifle. The villagers retreat.
Lawrence: Thank you.
Sir John: You can thank Singh. Whenever he gets back from the village. You're not the only one in this family who can act.
Lawrence continues noticing all his senses are now enhanced. His wound has healed at an accelerated pace, he had the strength to hold off those three men, and he can hear Gwen's heartbeat. He's feeling restless as he stares at her to the point it disturbs him and he excuses himself. She is left there confused by his behavior at that moment. In his room, he becomes alarmed when he looks at his wound and it's now completely healed.
Gwen: What's happened?
Lawrence: You have to leave. Please pack your things.
Gwen: Did I do something?
Lawrence: It's not safe here. You must return to London tonight. I'll be out here waiting.
Gwen: What are you afraid of?
Lawrence: If anything ever happened to you I'd never forgive myself.