The film opens on a dream sequence of Heather/Sharon in the Lakeside Amusement Park. She ends up on the carousel and is confronted by Alessa who proceeds to burn her to death. She wakes up and we get a little backstory that she and her father have been on the run from something and are just moving into another new house.
Chris/Harry sends her off to her first day of school. On the way she sees a bum who looks twisted to her at first, and ends up bumping into private investigator Douglas. He tries to question her but she flees.
At school we are introduced to Vincent, another new classmate. Heather leaves and begins to hallucinate memories of Alessa's childhood as well as a twisted school hallway with a lying figure monster that chases her. Vincent ends up showing up to snap her out of it.
We get flashback from Harry as to how Sharon/Heather was returned to him. Apparently Rose located a seal, only half of a two part medallion, that allowed her to send Sharon out of the fog world. She tells Harry through a mirror, and warns him not to return to Silent Hill.
Outside school, Douglas waits for Heather.This prompts her to call her father and tell him she thinks she's being followed. He tells her to head to the mall and he'll meet her there. Upon telling her, someone tries to break through the front door, so Harry heads out the back, only to still be taken by someone. The film cuts to Heather at the mall, who again begins seeing things twist into dark versions of themselves, including a clown and a child's birthday party. Douglas appears again and Heather fless, seeing increasingly strange things as she goes. Douglas follows, eventually confronting her in a dark alley where he tells her he was hired to find her, not because Harry mudered a man in their previous home, but because the cult, The Order of Valtiel, hired him to locate her. Douglas realized that he was working for something not quite right, and tries to warn Heather. In the ever twisting world around Heather, a blades monster shows up and chases the pair, eventually kiling Douglas. At this point Heather manages to return to reality, and quickly leaves, leaving her bloodstained jacket behind.
Outside the police find Douglas and take his body away, also finding Heather's jacket. Vincent appears and she leaves with him before anyone can recognize her. The two walk to Heather's house, Vincent talks about his grandfather Leonard, who is confined to a mental institution by his daughter, Claudia. Heather stopping to observe several cloaked figures that fade in and out on a bridge. Vincent claims not to see them and they continue. Heather leaves Vincent and goes inside the house, only to find a Halo of the Sun and the words "Come to Silent Hill" written in blood on her wall. She screams and Vincent come sback to find out why she did. Heather retrieves a box from her father's closet full of information on her birth, on the town, and the cult. As she begins reading the police arrive, so the two leave out the back. they take Vincent's car and head out for Silent Hill.
Heather reads several notes regarding the Order, who despite being seemingly Christian in the first film, actually burned Alessa as a test. If she survived, she would be used as the vessel to birth the God of the Order to cleanse the world. The notes also tell of Pyramid Head, Alessa's protector. Lastly, she finds a note addressed to her (as Sharon), which tells of Harry's attempts to hide her, his reasons for lying to her about her past, and how she should not go to Silent Hill under any circumstances. After hearing the note, Vincent decides he is too tired, and convinces Heather to stop for the night at Jack's Inn, not far outside Silent Hill. She protests, but Vincent convinces her to stop. In the room he pleads with her not to go, teling her it is a terrible idea. Heather doesn't want to listen, only wanting to find her father. Vincent then reveals himself as a child of The Order, sent to find Heather and return her to Silent Hill. He reveals however that although he was taught to hate Alessa and Heather, he doesn't see ehr as evil and pleads with ehr to leave. He tells her the other half to the seal that brought her back, and that is the key to saving her father is with his grandfather, in Brookhaven Asylum in Silent Hill. Before she can do anything, Heather's anger brings the darkness, which eats away the hotel room and transforms everything around them. The disc monster returns and takes Vincent. Heather is knocked unconscious.
She awakes in the morning, and realizes she has to go to the town. She sets out into the for. We get the shot sof her going past the famous Silent Hill sign. Once in town, she sees several people staring at her through windows. Eventually she approaches the church, where she meets Dahlia. Dahlia tells her more about Alessa and who Heather is, before the sirens blare and the darkness begins overtaking the town. Almost all the rest of the film is spent in the dark Silent Hill. Heather runs from the transforming town into a mannequinn warehouse. She happens upon one woman on a table who is transforme dinto a mannegquinn before her eyes. A second is wrapped in some sort of web, and Heather manages to free her. Upon freeing her, the mannequinn spider monster shown in the trailers wakes up and chases the two. They weave through several shelves in an attempt to reach the exit. The exit is locked, so the move towards a grated vent. The monster knocks a shelf ove ron the two, and tries to grab them. Heather makes it but the other woman is pulled away screaming by the monster.
After escaping to the outside, she finds herself near Brookhaven, and decides to find Leonard. She searches files at the front desk and locates his room, as well as takes a key. A prisoner monster attacks her, and she manages to shoot it. She continues on and finds Leonard, a blind old man chained inside his room. He tells her about himself, and that his grandson has also just been brought into the asylum. He asks to hold the seal so he can tell her what it is. When he gets it however, he jams it inside himself, gaining his sight and transforming into a large monster. He knocks Heather out and breaks out of his cell, taking Heather with him. As he carries her, she wakes up, She sees the complete seal inside the hole in his body. She reaches in and rips out the seal, causing Leonard to drop her and die.
Two Order members wheel Vincent into a room full of nurses. Apaprently, they are no sensitive to noise rather than light. The nurses murder the Order members, leaving Vicnent strapped to the table. If you've seen teh Comic-con clip, you know this scene. Heather rescues Vincent, and he agrees to take her to the Amusment Park, where the Order has a secret sanctuary underneath. They go in together, but Vincent decides to use himself as a distraction and lead several members away. He kisses Heathe rbefore he goes. Heather than makes her way to the carosuel. Pyramid Head is chaine dinto the machine that lowers it into the sanctuary. The Order members surround it, but a fire starts and sets many of them on fire. The dark Alessa shows up, ready to rejoin with Heather and destroy any good left inside ehr. In a very strange scene, Heather rejoins with Alessa by overpowering the evil, the good prevailing and making Heather the dominant Alessa. After this she arrives inside the sanctuary. Harry is chained to a alrge statue of Valtiel in the room. She meets Claudia, leader of this sect of the Order who tells her she is to be the vessel of God. Heather hands her the seal, and tells it to reveal her true nature. Claudia's skin bruns away revealing the blade monster. The rest of the Order flees and the monster gets ready to attack. However, sensing Heather in dnager, Pyramid Head appears and begins to fight the blade monster. The Blade monster gets some decent hits in, but eventually Pyramid Head prevails, slicing off the Blade monster's head. Heather, Vincent, and Harry escape.
The darkness finally leaves, and returns them to the fog world. The trio prepare to leave, but Harry tells Heather that he intends to stay. He believes Rose is still alive in Silent Hill somewhere. Heather tries to stay and help, but he tells her to leave, wishing a normal life for her.He says that even without Alessa, Silent Hill has a power, that it is a place of lost souls. Earlier Vicnent mentioned that that different people have different nightmares in the town. With that Harry leaves into the fog and disappears. Heather and Vincent leave, eventually making it to the highway outside of town. They manage to stop a truck driver, Travis Grady, who tells them he "hasn't been this way in a long time." They truck pulls away into the distance. The camera lingers as a police car, escorting a Toluca County prison bus, drives by past the Sielnt Hill sign as the fog slowly creeps back from the town.