Devki Sabarwal(Sridevi) is a biology teacher in a New Delhi school. Her step-daughter Arya happens to be her student. It so happens that one of the boys in the class has a crush on Arya and he keeps sending her messages—sometimes even lewd ones. On one occasion, Devki sees one of those messages and she throws the boy’s phone out of the class. Naturally, he is angry with the teacher.

At home, one can see that the relationship between teenage Arya and Devki is stressed. Arya calls her `mam’ instead of Mom. However Devki cares as deeply for Arya as she does for her natural-born younger daughter Priya.

Her husband Anand also tries to neutralize the equation between his wife and his older daughter. However Arya is stubborn.

One day Arya requests her father that she be given permission to go to a party at a farmhouse with school friends. Anand is due to leave on a business trip to USA for 10-days so he refuses permission initially. However Arya convinces him that she will be back home by midnight and he allows her to go.

At the party, Arya dressed in a smart red outfit is seen having a good time. She has a couple of alcohol shots and is dancing away. She spots a boy she has a crush on. However the boy is involved elsewhere so she is dejected.

She decides to leave the party but since her best friend is too drunk, she calls for a cab. Around the same time, the school boy whom Devki has reprimanded spots Arya. He asks for a dance. However Arya refuses. The youngster complains to his cousin Charles Dewan about this rejection. Charles, Jagan(Abhimanyu Singh), Baburam, a watchman help the youngster kidnap Arya. In the car she is physically violated and thrown out in a gutter.

A morning jogger spots her and gets her to a hospital.  In the meantime, Devki goes to the police station asking them to trace the whereabouts of her missing daughter, the cops are slightly unhelpful but they do promise to find the child. At the cop station is Dayashankar Kapoor aka DK (Nawazuddin) who hears Devki. He meets her outside and tells him that he too is the father of a young girl and if she needs any help from him, he will be happy to help. Devki ignores him initially.

At the hospital Devki breaks down when she sees Arya’s condition. She calls Anand and asks him to return home.  The rape case comes up for hearing on the fast track. However, the four accused manage to get away free for lack of substantial evidence.  Devki is unable to sleep. She badly wants revenge. So she contacts DK to help her find information about the four rapists. Francis Mathew (Akshaye) is a cop on the case. He too starts gathering info because of the unfair trial.

DK helps find out little known habits of the four criminals and Devki goes about eliminating them one by one.  Baburam is castrated; Charles is fed cynide and his cousin is put in jail on suspicion of poising Charles. The only one who moves around free is Jagan, Charles driver and the main criminal.  DK is about to close in on Jagan, when Jagan discovers he is being tailed.

At the same time Francis also discovers that Devki is somehow connected to the death of Baburam and Charles.  In the meanwhile, Arya who has recovered is taken to Kufri for a short vacation by her parents Anand and Devki.