The movie opens with a girl carrying a small black box into a living room with a fireplace. She sets the box down and attempts to start a fire to burn the box. A man, Robert, runs in and begs the girl to stop. The girl finally lights the match, which is then blown out. Robert cries out that "she doesn't know what she's doing!" An unseen assailant attacks the girl, forcing her to kneel on the ground. Robert is thrown from the room as ice moves across the floor and up the girl's arm, freezing her to the ground. The door then slams shut.
The scene switches to three friends - Jim, Ginger, and Dixie - who have just left a sorority-run haunted house at their college. Jim attempts to flirt with one of the sorority members, Ellen, until her boyfriend Tyler shows up. The three friends go back to Jim and Dixie's dorm room. While surfing uBid, an eBay-like auction site, Jim finds that someone is selling a small black box; inside the box is supposedly an 18th-century Irish servant girl who will do whatever her owner asks her to do. Jim begs his friends to help him buy the box for fun, and Dixie caves. Another bidder, Ghost_Hunter, fights Jim for the box, but in the end Jim wins. When the package arrives, the three friends open it together. Ginger wishes for a single red rose while Dixie merely wants his forty dollars back from Jim, who doesn't wish for anything. Jim opens the box to find nothing but a locket, with a picture of a girl inside.
Robert is shown in what appears to be a train depot. He receives a phone call from someone he addresses as "Amy," and tells her that "it's over." They begin arguing before she hangs up on him. Robert goes into the restroom, where he begins coughing and clutching his throat. He is then thrown up against the walls repeatedly until he screams, "The matter is closed!" He is dropped to the floor and left alone.
Ginger enters her dorm room and finds a single red rose laying on her bed. Meanwhile, Jim and Dixie enter their dorm room to find forty dollars - the exact amount of money Jim owed Dixie for the box - laying on Dixie's bed. That night, Jim sees a shadowy figure that disappears in the direction of the bathroom. Jim wakes Dixie up and tells him that someone is in their room. They run into the bathroom to attack the intruder when they hear their room being ransacked. When they go back into their bedroom, the beds are overturned and their belongings are thrown everywhere. Two TAs enter the room and tell Jim and Dixie to keep it down, clean their room up, and pay for the damage to the wall. Upon inspection of what they mean, they find words in a language they don't understand scratched into the wall.
The next day Ellen approaches their lunch table and asks for help with a children's Halloween party her sorority is throwing, and Jim agrees. Ginger becomes upset with Jim over the attention he gives to Ellen. Jim tells her not to "break up the family" and she snaps that they're not a family. She goes back to her dorm room and finds someone curled up in her bed with the blanket pulled over their face. Thinking it's her roommate Misty, Ginger pulls the blanket back only to find the bed empty. The books on the shelf above her bed are pushed off, followed by her lamp and other belongings.
The next day Jim takes a picture of the mysterious writing on the wall. He takes it to a friend of his, Kendal, who tells him she needs time to figure out its meaning. Outside in the hallway, Ginger and Jim watch as Professor Haskell, one of Dixie's professors, accuses him of plagiarizing another student's paper. That night, Professor Haskell is working late and hears someone outside of her office. She decides to leave, but as she heads down the hallway she hears someone following her and suddenly begins to spit up blood. She is then forced up against the wall and her tongue is pulled out of her mouth; we see her bite down on her own tongue.
Ginger knocks on Jim and Dixie's door and asks to stay there for the night because she is too creeped out in her own room. Ginger brings up the box, and asks Jim if he thinks it has anything to do with what's been happening. Jim insists that the box is just a toy. The next day, Ginger notices that Misty is wearing one of her (Ginger's) sweaters, and comments on it; apparently Misty has a habit of taking Ginger's clothes. Misty seems flustered and leaves. Ginger and Jim follow a crowd of students to a hallway where paramedics are pulling a covered body on a stretcher. They find Dixie in the crowd, who tells them that Professor Haskell was found dead; she appeared to have gone insane and cut her own tongue out, bleeding to death. Jim receives a phone call from Kendal, who has figured out the writing on the wall. She tells him it's Gaelic, an 18th century Celtic dialect. The phrase translates to "A family or death."
In Misty's art class, the sweater she took from Ginger's closet becomes snagged on the desk. While she examines the tear in the sleeve, her hand is forced down onto the desk and a nearby paper cutter is dragged over in front of her. The professor, thinking that Misty is just goofing off, tries to tell her to stop, but she insists that she's not doing it as her arm is pulled across the cutter. The professor tries to move her arm but is thrown aside. Another student tries to help but is also pulled away just before the blade comes down on Misty's arm.
Jim emails Ghost_Hunter, the other bidder, and asks what their interest was in the box and if they knew anything about it. He then heads to the sorority house to help Ellen with the party. Tyler is also there. Jim receives a call from Ginger but ignores it. After a while, Tyler begins to clean up and asks Jim to help; when they are alone, Tyler threatens to kill him if he comes anywhere near Ellen again. Jim sends another email to Ghost_Hunter and describes the locket that came with the box. While he's examining the locket, he gets a phone call about Misty and quickly leaves the dorm. Meanwhile, Tyler is driving down the street at night when he sees a young girl in 18th century dress run across the road. He stops and asks if she's all right. The girl orders him to leave her alone. Tyler tells her that he needs to call her parents, but she again tells him to leave her alone or she'll scream. He tries again, this time handing her his phone to call her parents herself. The girl screams and Tyler disintegrates, and the young girl disappears.
Jim arrives at the hospital, where Dixie tells him that Misty lost a lot of blood, but is alive. Ginger is upset with him for ignoring her earlier phone call, plus others. She tells him to leave the hospital because it's all his fault anyway. In the parking lot, Dixie tells Jim that Misty's classmates described her as being possessed when she cut off her own arm. He tells Jim that it has to be the box, but Jim brushes it off and leaves. The next morning, Jim is awakened by a phone call from Ellen. She asks him if he knew where Tyler went after leaving the house the day before, because he never showed up at his dorm. When Jim starts to ask her on a date, she tells him to stop, and that if she were single she might go out with him. Jim hangs up and notices that he has an email from Ghost_Hunter. The email asks Jim if he opened the box or not. Jim examines the box again and finds a small compartment in the lid hiding the elegy of Katie Malone. The back of the pamphlet says "Beware."
Ellen is shown leaving her sorority house for a morning run, but becomes wary when she notices that no one else is outside. After a while she begins to hear noises. She suddenly feels herself getting pulled and pushed in different directions, and eventually runs under a bridge where she is attacked some more by an unseen assailant. Ellen is then picked up and tossed around before finally being pulled apart. Jim searches for the story of Katie Malone on the internet, and finds a website fully devoted to an Irish urban legend about her. A picture on the website of Katie exactly matches the one in the locket they found inside the box. He asks Dixie and Ginger to meet him in the library to talk. On the way there, he comes across members of Ellen's sorority crying and comforting each other, sitting beside the two TAs from his dorm. He asks them what happened, and they tell him that Ellen was torn apart in the park.
At the library, Jim tells Dixie and Ginger about Ellen, and then says that the ghost of Katie Malone was behind it. He shows them the elegy pamphlet he found in the box, and tells them the story he found online. Katie Malone was an Irish girl brought to America to work as a servant, but was repeatedly beaten by all of her owners. Her last owner would tie her up and leave her in the barn overnight, but his youngest daughter would come out and bring Katie food and blankets, acting as the only family Katie had. One night she gave Katie a small box and told her that it was used to house the spirits of family members. When her father found out, he beat both his daughter and Katie, and again left Katie tied up in the barn. The next morning she was found frozen to death. The farmer's daughter ran away, taking the box with her with Katie's soul inside. The following day, the farmer was found dead with a phrase carved into the floor near his body, the same phrase that was carved into the dorm room wall: "A family or death."
Jim tells them that they have to act as a family, what Katie wants, but Ginger suggests that they set her free instead. Jim puts his hand on the box and tries to tell Katie's spirit that she's free and they don't own her anymore; he suddenly jerks his hand back as if burned, and tells his friends that he thinks it worked. As they leave the library, he throws the box in the trashcan.
After a couple of days, Ginger and Jim go out on a date together, then back to Ginger's dorm. Ginger goes into her bathroom to freshen up; when she leaves the mirror, Katie's ghost appears behind her and comes out of the mirror. When the bathroom door opens, Jim expects to see Ginger but instead sees Katie's ghost approaching him. He falls off the bed and hides under Ginger's desk, only to see that he was hallucinating and it was in fact Ginger. She asks him to leave. The next day Jim apologizes and Ginger assures him that everything's all right.
The college's Halloween party is that night, and Dixie leaves the dorm while Jim is still getting ready. Alone in the dorm, Jim notices that he has a new email from Ghost_Hunter, who tells him that they need to talk to him immediately and to send his phone number in an email. He does, and a few moments later Jim's phone rings. He answers it, and a girl - Ghost_Hunter - tells him he's in danger. Jim tries to explain that they set her free because people were dying, but Ghost_Hunter tells him that now Katie's going to kill all three of them. Jim tries to leave his room to get to his friends, but finds himself locked in. He turns to find the box sitting back on his desk.
Ghost_Hunter tells him that only way to get rid of Katie is to sell her, and she says that she'll be the one to buy her. Jim sets up a five minute auction for the box on uBid. At the party, Ginger, tired of waiting for Jim, tells Dixie that they should go see if he's all right. Before they can leave, other students are thrown across the room and ice moves across the floor in their direction. They attempt to find a room to hide in, but all of the classrooms are locked. Eventually they make their way into what appears to be a large maintenance room, and can hear footsteps in the walkways above them. When Dixie places his hand on a metal railing, ice appears and freezes his hand to the metal. He pulls his hand free, pulling skin off of his hand. The footsteps get louder, followed by a loud scream. They make their way to another door and leave the room right as the auction for the box ends. Dixie and Ginger run into the school gym and collapse on the floor. Dixie tells Ginger that no matter where they go, Katie Malone will find them. Ginger hugs him, and the lights go out.
In the darkened gym, Dixie lights a lighter and Katie appears behind him. The lighter goes out. Ginger finds it and relights it, only to find a pool of smeared blood where Dixie had just been. She sees the light from the hallway through the cracked doors and heads for it, falling against the opposite wall out in the hallway. Her hair is suddenly pulled, dragging her across the floor and towards a garbage can that had been pushed over. She stops only inches from a wooden plank with nails sticking out of it. Jim runs down the hall and tells Katie that he sold her and it's over. Katie screams, shattering the windows. When she finishes, Jim and Ginger sit on the floor of the hallway holding each other.
Ghost_Hunter holds the box, telling Katie that she'll never let her out so she can never kill again. Someone knocks on her bedroom door and she shoves the box under her bed. Robert, from the beginning of the movie, comes in. It's revealed that Robert is her father, and she is the Amy that he had argued with on the phone. In the mirror, Robert sees the box underneath Amy's bed. He confronts her and she tells him that she won't let Katie hurt anyone. When she tries to take it back, it slips from Robert's hand and falls onto the floor, opened. After a pause, Amy's bedroom door slams shut.