Buppah Rahtree is a loner female student at a Bangkok university who becomes the object of a wager by a group of male students to see if she can be bedded. Ake, the son of a wealthy family, takes the bet and courts young Buppah. She resists him at first, but one day sees him feeding pigeons in a park and goes to talk to him. She remarks that in her next life she hopes to become a bird, so she could fly away. Noting his BMW convertible parked nearby, she goes on to say that if she had a way, she would fly away right now. So Ake takes Buppah for a ride down the highway. They continue to have a relationship, which culminates in a three-day weekend at Bang Saen, during which Ake has sex with her and stays in bed with her the whole time.
Ake had videotaped their sessions and upon his return to Bangkok, he shows the tape to his friends. He has succeeded where the others failed and for his efforts, he wins a bottle of Johnnie Walker, which he reflects to himself seems like a trivial prize for messing up another person's life. Ake then breaks off all contact with Buppah, who finds she cannot reach him by phone.
One day she is given a ride in a car by her stepfather, who takes Buppah to a short-time hotel and sexually assaults her. She stabs her stepfather with her fountain pen, that was given to her by her stepfather as a present and runs home to her apartment, room 609. Depressed, she decides to commit suicide and is about to cut her wrist with a utility knife when the phone rings. It is Ake and he wants to meet her. Ake informs Buppah about the wager with his friends and apologizes. He then informs her that he is to leave Thailand to study in England, but he hopes he and she can still be friends. Buppah then informs Ake that she is two months' pregnant. Ake is directed by his mother to convince Buppah to have an abortion. He brings her back to her apartment after the operation, and she is in obvious pain. He says he is going to get her some rice congee, but he instead gets in his car and drives away and then leaves the next day for England.
Buppah is living an apartment block managed by Mrs. See. One day Mrs. See tries to collect rent money from Buppah, who answers the door and looks weak, but says she'll pay the rent the next day. The next day passes and the landlady goes to investigate. She finds Buppah's door locked and chained. Using a hacksaw, Mrs. See's brother gains entry to apartment 609, and he discovers Buppah's corpse in the bathroom. Buppah has bled to death due to complications from the abortion.
The police come, along with a spiky-haired female medical examiner, and the rescue squad, to retrieve the body. However, when the rescuers try to carry Buppah's body out, she starts moving. They put the corpse on the bed, and she sits up, scaring the rescue men, who run screaming from the room. The police are then sent in to retrieve the body, but they, too, are rebuffed. Buppah's vengeful spirit refuses to be dislodged.
The apartment block is home to a false shaman named Maew, who puts on a daily act and earns quite a bit of money for Mrs. See. To make people believe he is real, Mrs. See convinces Maew to try and exorcise the ghost. After he fails, he convinces his teacher, Master Tong, to try. For his effort, Master Tong is left with a knife in his back.
Then, a pair of Roman Catholic priests try to perform an exorcism, but only end up having obscenities shouted at them by the ghost, who also vomits a liquid akin to pea soup on one of the priests.
Buppah's ghost runs wild throughout the apartment block. One night, she haunts every bathroom in every room. Her death by bleeding is re-enacted, with black blood flooding the hallway. Residents leave in droves, ruining Mrs. See's finances.
Meanwhile, Ake has grown homesick in England, and has turned to drug use. He wants to come home. He then appears at Buppah's door, and offers to bring her some rice congee. Ake catches the eye of Muay, a young woman at the congee stand. Muay seduces Ake, and has him take her to an old movie theater, where they have sex. When Ake returns to Buppah's apartment, he has forgotten the congee. Buppah knows that Ake has cheated on her, and for his transgression, she amputates his legs with the hacksaw that had been left behind by Mrs. See's brother.
Muay later comes to the apartment to find Ake. Buppah takes possession of Muay's body and starts to have Muay cut her own legs off with the hacksaw.
Mrs. See still wants to get Buppah out of her building, so she has summoned a genuine shaman from Cambodia. The shaman and his men come to the apartment just as Muay is being possessed. They put a spirit cloth over Ake and on Buppah's corpse. Through a prayer, the shaman is able to get Buppah's spirit back into the corpse. They then plan to take Buppah to a temple to be cremated, but on the way, the spirit cloth blows off the body, which is in the back of a pickup truck. Buppah takes control of the vehicle and causes it to crash into another truck.
Muay, saddened by the turn of events, makes contact with Ake's father, who is angered and puzzled by the call. As it turns out, Ake has been dead for more than a month. Muay had sexual relations with Ake's ghost.
Buppah is back in apartment 609, where she will likely stay for eternity. Ake's ghost, now legless, sits outside in the hallway, and apologizes to Buppah for the rest of his ghost eternity.