Bobo (Emraan Hashmi) is India's top magician, a star. But unknown to even his beautiful girlfriend Tamara (Huma Qureshi), his life is falling apart. Hallucinations about his dead little sister Misha are casting a dark shadow on his life, threatening his very sanity. He is shown to be frequently drawn to his old vacant family apartment, where in the latest visit, he opens the lid of a treasure chest in one of the rooms, only to see a vision of his little sister Misha dead inside with a lizard crawling over the body. Tamara tracks him down to the apartment at the same time, taking him back to the room and opening the chest, only to find Misha's old doll inside. This latest hallucination proves to be too much, and Bobo is left with no option but to seek psychiatric help in the form of the rather odd Dr. Palit, who puts him under regression hypnosis to go back to the distant past, when Bobo was 11 and Misha 6.A terrifying childhood story surfaces in which a dark supernatural power, in the form of a Daayan (witch) enters the lives of the two children and their father. Bobo and Misha are shown to live with their Dad in the family apartment with their mother having died some time earlier. Bobo is seen reading a book of Witchcraft from which he discovers the number 666 and uses it to travel on the apartment elevator to some unlisted floor at the bottom of the building, which he confides to Misha as being the entry to hell. According to Bobo, each building has its own hell, where the "bad people" of the building are consigned for eternity once they are dead. Soon after Bobo and Misha's trip on the elevator, a woman named Diana (Konkona Sen Sharma) moves into the building. Bobo is convinced that she is a witch and that she has surfaced from down under following his and Misha's trip on the elevator.Diana immediately charms Bobo's single father and agrees to babysit the kids. She soon becomes a part of the family by marrying Bobo's father, although the paranoid Bobo still believes she's a witch. Meanwhile, Bobo learns from the book that the source of a Daayan's power is her plait, while that of a Pishacha is his neck. On Diana's birthday during the night of the red moon she convinces the kids to a game of hide and seek in an attempt to sacrifice Misha in order to restore her dark powers. As she begins to look for the kids, Bobo peeks through his hideout to see what she's doing. Bobo's father returns claiming to have forgotten his files and goes to look for them while Bobo goes to check on his sister. Finding the door locked Bobo begins to panic which brings his father to the door. Bobo's father knocks down the door only to find Misha lifeless in the trunk and a now undisguised Diana hovering over her body. Enraged, Bobo's father attempts to choke Diana but in vain as the now rejuvenated Diana kills him with her ear-piercing screams. Diana moves to the window to perform the rest of her ritual. But the distraught Bobo finds his father's dagger and cuts off Diana's plait, destroying her source of power. A shocked Diana begins to crumble into dust but not before she reveals that everything she did, she did for him and promises to return for Bobo.