Kaun?
A young woman (Urmila Matondkar), home alone, is watching the news of a serial killer on television when the doorbell rings. The woman sees through the peephole that it is a young man, who later identifies himself as Sameer A. Purnavale (Manoj Bajpai), claiming to be a business partner of Mr. Malhotra. She is reluctant to open the door, due to the news of a killer on the loose. The woman claims that the house doesn't belong to Mr. Malhotra but to Mr. Gupta. However, the man believing that there has been a mix up, persistently keeps ringing the doorbell even after the woman tells him that she won't let him in. To scare him away the woman lies and tells the man that her husband is sleeping upstairs. The man then claims that he hears a noise upstairs so that if her husband is awake can he talk to him. Upon hearing this and a subsequent noise from within the house, the woman is spooked and runs outside. Punarvale then takes the woman back inside, reassuring her that he is protecting her.
When no one is found, she asks him to leave, and opens the door, only to finds another man with a gun, who later identifies himself as Inspector Qureshi (Sushant Singh). The two doubt his credentials, and Qureshi phones the police station and calls for help. The two men then get into a fight, and during the struggle the woman gets a hold of Qureshi's gun, and asks them to sit quietly. It is then revealed that the man claiming to be Inspector Qureshi is in fact a thief. The woman telephones her mother and asks her to contact the police.
Sameer tries to kill Qureshi, thinking that he is the serial killer and then uses the telephone to call the police, however he finds that the phone is not working. He is unable to understand what is happening and asks the woman to hide somewhere safe inside the house while trying to figure out a solution to the problem. The door bell rings and Purnavale answers. He starts looking around for the woman, calling out to her that there was a man asking for Mr Malhotra and is confused because the woman claimed when they met that the house belongs to Mr Gupta. Whilst searching for her in the attic, Sameer stumbles upon a dead body and identifies it as that of Mr Malhotra. Sameer panics and when he looks around the woman attacks him and in self-defense he tries to kill her. In this confusion the thief who is wounded stabs Sameer to death to save the woman, assuming that Sameer was the killer. Whilst the thief checks on Sameer's body, the woman begins humming and stabs the thief to death.
At the end of the movie it is established that the woman is mentally ill as she cleans up the bodies and rearranges the furniture and proceeds to talk to her "mother" using the disconnected telephone. Before the credits it is shown there is another man at the door asking for Mr. Malhotra, she then turns to the camera and smiles ominously.
murder