The movie opens in 1969 with the parents of a young Spanish boy rushing to the presence of channeller Shaun San Dena (Flor de Maria Chahua). Their son had stolen jewelery from a band of gypsies in town, and since then, he had been complaining of seeing and hearing things not of this Earth. San Dena tries to help the boy in a seance, but she is beaten by an unseen force, as are the young boy's parents. The force throws the boy from the second floor down to the first. The boy survives the fall, but as his parents rush down the stairs to tend to him, he is physically dragged to Hell through the floor by demonic hands. Several years later, we are introduced to Christine Brown (Alison Lohman), a loan officer with a promising future. A position for assistant manager has opened up at the bank at which works Christine and both she and her co-worker, Stu Rubin (Reggie Lee), are up for the promotion. Christine's boss, Mr. Jacks (David Paymer), advises her that she needs to demonstrate that she can make tough decisions and hard calls when she needs to. That same day, Mrs. Ganush (Lorna Raver), an elderly Gypsy woman, asks for a third extension on her mortgage because she is struggling with her economic problems due to her sickness. Christine, after a private talk with her boss, Mr. Jacks, denies Mrs. Ganush the extension against her better judgement only to prove herself to her boss. In desperation, Mrs. Ganush prostrates herself before Christine, begging and kissing the hem of her skirt. As a crowd of customers and employees gathers, Christine panics and shoves the woman away, shaming her in public. A pair of security guards then grab Ganush and walk her to her yellow car. Mr. Jacks compliments Christine on how she handled the situation and tells her the job will soon belong to her, but asks her to take care of a large loan in the works for another client before he can promote her.
That night, in a parking garage while Christine is walking to her car, she notices Mrs. Ganush's yellow vehicle parked across from where her own is parked. Christine enters her car and realizes that Mrs. Ganush is staring straight at her in the back seat. Mrs. Ganush attacks and Christine tries desperately to fend her off of her by driving the car into a cement wall. Mrs. Ganush is now in the passenger side of the car and still attempts to attack Christine until she finally kicks the old woman out of the car and immediately closes and locks the door. After the frightful battle with Christine, Mrs. Ganush vanishes below the window, only to reappear with a cinder block. She uses it to break the passenger side window, and then pulls Christine from her car. After a short struggle, Mrs. Ganush removes a button from Christine's jacket. Mrs. Ganush places a curse upon the owner of the button and says to Christine "Soon, it will be you who comes begging to me," and gives the button back to Christine before leaving in her car. The police arrive, and Christine's boyfriend, Dr. Clay Dalton (Justin Long), arrives to comfort her. On the way home, they pass a fortune teller's store, and Christine insists they go in. There, they meet the fortune teller Rham Jas (Dileep Rao), who tells Christine that she has a dark spirit upon her.
Back home, Christine is left alone with her pet kitten, Mr. Kitty, whilst Clay goes to deal with Christine's car. There, Christine is set upon by the aforementioned dark spirit, which appears as the silhouette of a goat's head. The spirit breaks some windows, cuts the power, and throws Christine across the room, causing minor injuries. Clay assumes that Mrs. Ganush followed them and attacked Christine again. However, when she insists that no one attacked her, they contact a psychologist. The psychologist says that victims of assault often relive past trauma, which seems to settle Christine. It is later revealed that Mrs. Ganush had passed away after the meeting with Christine.
Christine has several frightening visions of Mrs. Ganush's deformed and malevolent spirit, making her life a living nightmare. At work, she upsets Mr. Jacks and her fellow employees with her bizarre behavior. With nobody to believe her, Christine makes a last desperate attempt to prove her sanity by consulting Rham Jas again, who tells her that she has been cursed and that she is to be tortured for three days by a demon called the Lamia before being dragged to Hell to burn for eternity. Horrified by this revelation, Christine begins a race against time to save her soul from damnation, trying various methods to beat the curse including sacrificing her kitten and paying 10,000 USD to enlist the help of Shaun San Dena (Adriana Barraza), who calls forth the Lamia during a seance. (While attempting to find the money, Christine discovers the bank has lost the large client to another bank and neither she nor Stu Rubin will not get the promotion.) The goal of the seance is to transfer the Lamia into a live goat, then kill the goat, which will destroy the Lamia. The Lamia takes control of nearly all those involved and claims it will not rest until it takes Christine's soul to Hell, but is banished by Shaun San Dena, who then dies from the experience.
Saddened, but relieved to believe it is finally over, Christine is shocked when Rham Jas tells her the Lamia was only banished from the seance; it will still return to claim her soul in just one more day unless she can find a way to stop it for good. He then tells her the only way to get rid of the curse is to give the cursed item to someone else as a gift, thereby cursing them. Christine seals the button from her coat in an envelope and fights with her conscience over whether she should give it away, as it would be condemning the owner to an eternity in Hell. Deciding she cannot go through with giving the envelope to a living person, Christine finds Rham Jas and asks him whether it would be possible to give the curse to a person who is already dead. He tells her that souls live on even after the body stops living, and that it would indeed be possible to pass the curse on to someone dead. Christine decides the only person who deserves to be given the curse is Mrs. Ganush herself, though she very nearly gives it to Stu Rubin. It is discovered he is responsible for costing their bank the large client by giving the loan to another bank and attempting to pin the theft on Christine. She drives to the graveyard to find the corpse of Mrs. Ganush and is attacked along the way. Eventually she finds the grave and starts to dig it up, but the ground caves in around her as she passes on the curse, almost engulfing her as the crucifix on the tombstone falls on top of both her and an inanimate Mrs. Ganush. She successfully plants the envelope into Mrs. Ganush's mouth, formally giving it as a gift, and escapes from the graveyard.
Relieved, Christine goes to the train station the next day to meet Clay, who is preparing to propose to her. However, upon greeting her on the platform, he shows her an envelope, the envelope with the cursed button. The envelope Christine had grabbed in his car contained the rare Standing Liberty Quarter she had previously given him, and the coin was the gift she gave Ganush instead of the button. Horrified, Christine stumbles backward and falls onto the tracks as a train is approaching the station. Just before she is struck, the ground beneath her opens and demonic arms grab her from below, pulling her down, burning and screaming, into a fiery Hell. As the train roars through, Clay can only watch, frozen in terror.