The film starts with Krishna Verma (Vidya Balan) trying to convince her husband, Vidyadhar Verma (Adil Hussain), a local gang-lord, that he should surrender. He agrees, but is soon killed in a gas explosion. Two criminals Iftikhar aka Khalujan (Naseeruddin Shah) and Razzak Hussain aka Babban (Arshad Warsi) botch up a job and escape from the clutches of their boss Mushtaq (Salman Shahid), who wants to bury them alive. They land up in Gorakhpur in Uttar Pradesh to seek refuge in the house of Vidyadhar Verma.Instead they meet his widow Krishna, who gives them shelter and tries to seduce both of them in order to achieve her own secret goal. She proposes the kidnapping of Kamalkant Kakkar aka KK (Rajesh Sharma), a small businessman. The duo reluctantly agree, since they want to escape the clutches of Mushtaq. Khalujan and Babban meantime realize that they are falling for Krishna, but they do not reveal their feelings to each other. Khalujan decides to tell his feelings to Krishna, but is shocked when he sees Krishna and Babban having sex. Khalujan is angry, but keeps quiet. However, when the kidnapping does not go as smoothly as wanted, Khalujan and Babban start fighting.Meanwhile, Krishna tortures KK and asks him where her husband is hiding, revealing that Verma might be alive. KK finally calls Verma. Both Babban and Khalujan realize that Krishna was just using them. They confront her, whereupon she reveals that KK and Verma were partners in the illegal business and that Verma is still alive. The duo reach KK's factory and are shocked to find Verma. Verma's goons blindfold the duo and take them to a deserted spot. When they take out their blindfolds, Babban sees Nandu (Alok Kumar), a boy he had previously met, pointing a gun at them. However, Nandu leaves them alive and explains the whole story. He tells that Verma had no plans to leave his criminal life, so he faked his death in front of Krishna, so that she would think he is dead.Khalujan and Babban race back to Krishna's house, where they have left her tied to a chair. Meanwhile, Krishna succeeds in opening the tube of gas cylinder, causing a gas leak. Verma confronts her and she tries to kill both of them by igniting a lighter. Verma assaults Krishna while the duo arrives. Soon, police arrive at the scene too. Verma's goons are killed in a shootout, while Verma is killed in a gas explosion. The duo save Krishna and soon the trio is seen walking away from the burning house.Unknown to them, Mushtaq is pointing a gun at them. Suddenly Mushtaq's wife/mistress calls (whose voice is surprisingly similar to Krishna's). The trio are still seen through the gun hole of Mushtaq, thus making their fate unclear, although it can be assumed that Mushtaq left them alive.Cast and charactersNaseeruddin Shah as Khalujan/Khalu/Iftikhar, 51-year-old Khalujan is a pure romantic at heart. He is a bit of an odd cookie in the world of crime. Sure, he has a sharp mind and body and has been toughened up over the years living in the world of guns and gangsters; yet, he is very emotional and tender at the core. He wants to go back to his village and wants to settle down in a quiet, peaceful country life existence. Only, life had other plans for him. Love happens to him. Krishna happens to him.Arshad Warsi as Razzak Hussain aka Babban, 32-year-old Babban is in more ways than one, the antithesis of the kind of man his uncle is. If Khalujan is all heart and soul, Babban is all flesh and blood. He is hot-blooded, lustful and scoffs at the idea of true romantic love. Babban is cynical, indifferent to finer things in life and tough as nails. Through the course of the film, Babban discovers what it is to love and to be betrayed. It makes the dormant softer side of him come alive. Perhaps for the first time in his life, Babban cares, for Krishna.Vidya Balan as Krishna Verma, 30 years old, femme fatale, small-town girl, mysterious woman and forgotten widow; Krishna is a bundle of contradictions. She was seen as a woman madly in love, as an object of desire, as a vision of purity and engaging herself in a lustful bout with another man.Salman Shahid as Mushtaq Bhai, Master of Khalu and Babban; a cold-blooded criminal who is chasing the duo after they botched up his job, causing him loss of money. Due to him, the duo has to take refuge in Vidyadhar Verma's house.Anupama Kumar as Manju Kakkad, Wife of KK; a typical wife of a rich businessman and a clueless person in all the drama.Gauri Malla as Mamta (Nepali actress), Niece of a beauty parlor owner; runs a brothel in garb of beauty parlor; KK is her regular customer.Adil Hussain as Vidyadhar Verma, Husband of Krishna and an illegal weapons dealer; likes Krishna but does not want to stop his illegal business, hence he fakes his own death in front of Krishna.Rajesh Sharma as Kamalkant Kakkad aka KK, Founder of KK steel company, partner of Vidyadhar Verma in arms business; runs his arms business in garb of steel foundry.Alok Kumar as Nandu, A 15 year old boy and acquaintance of Babban. Is given a contract to kill the duo by Vidyadhar Verma, but leaves them alive and tells them the real story as he feels that Vidyadhar has done injustice to Krishna.
Output: Question: Krishna succeeds in opening the tube of gas cylinder, causing what?, Answer: A gas leak.