Vidya Sinha (Vidya Balan) is a middle-class working mother who lives in Chandan Nagar, West Bengal with her teenage daughter Minnie (Tunisha Sharma), who is paralyzed from the waist down and uses a wheelchair. Minnie is a happy child and Vidya dotes on her, working hard to save money so that she can take Minnie to the United States in the hope that the girl will walk again. One evening, Vidya returns home to find her daughter is missing. She receives a call from an unknown man asking her to come to an address, or else Minnie will die. When Vidya crosses the road, a taxi knocks her down, sending her into a coma. The taxi driver takes her to a nursing home run by Dr. Maity (Pradip Mukherjee). Police Sub-Inspector Inderjeet Singh (Arjun Rampal) is put on Vidya's case. He visits Vidya home and finds her diary, which he takes as evidence. Inderjeet's senior, Pranab Halder (Kharaj Mukherjee), informs him that a woman named Durga Rani Singh
is wanted for a kidnapping and murder case. As Inderjeet reads Vidya's diary, her past is revealed: She worked as a clerk in a school in Kalimpong as Durga Rani Singh, where she is friendly with Arun (Tota Roychoudhury), who has feelings for her. At school, Durga noticed that a student named Minnie Dewan (Naisha Khanna) was always punished for sleeping during classes. After repeated attempts at befriending the reclusive Minnie fail, Durga decides to visit the girl’s wealthy grandmother (Amba Sanyal), pretending to be offering Minnie extra tuition. Durga's worst fears come true when Minnie confides that her uncle Mohit Dewan (Jugal Hansraj) was sexually abusing her. Durga, also a survivor of child sex abuse, informs Minnie's grandmother but the woman admonishes her. Durga then tries to file a case with the police but an investigation by a police officer (Koushik Sen) finds Mohit innocent and he doesn't believe Durga. Minnie jumps off her house's terrace in d
esperation and becomes paralyzed from the waist down. A corrupt policewoman (Gargi Bharadwaj), taking the side of Minnie's grandmother, threatens Durga not to pursue the matter. Durga decides to save Minnie from her family and has a fight with her grandmother, who is killed accidentally. Durga flees with Minnie, settling in Chandan Nagar with a new name, Vidya Sinha. Years later, Mohit hunts them down and kidnaps Minnie with the help of the policewoman. In the present, the policewoman comes to the nursing home and threatens Vidya to pay ransom to save Minnie. Terrified, Vidya escapes from the hospital after recovering from her coma and returns home in search of the address that the kidnapper asked her to come to. She is caught by Halder and Inderjeet at her home but escapes after shooting Inderjeet in his arm. Vidya then arrives at Kolkata, where she goes to the docks as ordered by Mohit and offers to pay the ransom to the policewoman. Mohit shoots the policewoman when she takes
interest in the ransom money and then tries to strangle Vidya as revenge, but is shot dead by Minnie, who picked up his fallen revolver. Vidya then calls Inderjeet to seek his help, but Haldar and other police officers ask Inderjeet to call her to a place where they can arrest her. Inderjeet asks Vidya to come to his paternal house, where they are surrounded by the police force. Halder tries to arrest Vidya, but she shoots him in the leg and later sets the house on fire. It is revealed that Durga was married to Inderjeet at a very young age, but they separated later. After recovering from her coma, Durga asked Inderjeet for his help to save Minnie and they planned her escape. In the present, Inderjeet helped Durga in escaping to Kolkata in the police Ambassador car by smuggling her in the trunk, and he helps her escape from the burning house. Inderjeet also arranged passports for Durga and her adopted daughter under their new identities. In the end, Durga (who is believed to be dea
d by the police) is traveling to New York City for Minnie's operation. Inderjeet is seen happily driving with his family.