4 friends Kalim (Angad Bedi), Gautam (Neil Bhoopalam), Maya (Kangana Ranaut) and Abhay (Randeep Hooda) delve into what seems to be their "first case", having started a gang called the "Ungli" gang which fights against corruption. Their job is to bug corrupt people and teach them moral lessons quite unconventionally. They target a corrupt minister and become the most wanted people in Mumbai, but also earn the respect, affection, and admiration of the general public in the large metropolitan town.

Meanwhile, ACP Ashok Kaale (Sanjay Dutt) meets his superior, DCP Shivraman (Shiv Kumar Subramaniam) who introduces him to Police Commissioner Arvind Kaul (Raza Murad) with the task of deciphering the "Ungli" gang. Later, Kaale travels to another police station where he meets an amusingly frustrated officer, Kaale's colleague and bomb-squad commandant Mishra (Shishir Sharma), who is disgusted with the act of "crime" his recruit Nikhil Abhyankar (Emraan Hashmi) has done. Eventually, it goes so: a college was attended to by the bomb squad when there was news that a bomb was planted there. Nikhil took advantage of the situation and met his girlfriend (Rachel White) with whom he shared a kiss, but soon they were caught by the dogs of the Bomb Squad. Later, it surfaced up that the call was made from Mishra's desk, and Nikhil did it. Kaale finds it funny at first and points out the clever act Nikhil made, but when the officer reprimands Nikhil and himself, Kaale visits Nikhil's mother (Reema Lagoo) where she tells him that Nikhil had the qualities of his father, Kaale's colleague Arvind, and that Nikhil was raised by Kaale like his own son. Nikhil, it is shown, attends a disco bar, where Kaale calls him up to discuss matters concerning the "Ungli" gang.

Nikhil begins searching for altruistic opportunities to earn the "Ungli" gang great fame, once by blowing up the roads in front of a minister's house and accusing politicians and PWD workers of torturing the people by lavishly spending money on renovation of roads directly linked to houses and offices of politicians and corporates alone, another instance by putting up a label of dishonesty on the auto-rickshaw drivers by accusing them of charging high rates and showing reluctance when asked to drive to places close by. Finding him adamant, Maya suggests that Nikhil too has wished to join the gang, and on certain terms and conditions, the four friends admit Nikhil, and narrate the story behind the gang's formation.

Maya's brother Ricky (Arunoday Singh) was a great fitness freak and struck a rapport with the four friends quite a time. However, one day, while trying to prevent a scuffle between an old man (Avijit Dutt) and a bratty youngster Anshuman, Ricky tried to defend the old man, but Anshuman struck him hard, landing him straight into coma. The old man later decided to complain to the police, but was advised against it by the police itself, when a hunchback of Police Supremo B.R. Dayal (Mahesh Manjrekar), Anshuman's father, spoke so. The old man was firm, but when his granddaughter, while waiting at a bus stop, was threatened with an acid attack, the old man was forced to swerve from his stand to protect her. This plunged Maya into grief, but Abhay was angry at one of Maya's comments and this paved the way for the "Ungli" gang. Nikhil poses as a law student to illusion the four.

While preparing for a raid, Nikhil sprained his knee, but later called up Kaale when the four left. However, feeling remorseful, he later attacked Kaale to defend his new "friends", but when his identity was discovered, the four friends slammed him with Abhay hitting him hard, and Kaale further hitting him, but Nikhil later chides Kaale for believing the "Ungli" gang as a criminal force. However, when faced with a loss of duty, finding that DCP Shivaraman is trying to bribe him into getting a posting of choice to save ends, Kaale agrees with Nikhil, and seeks out the gang to expose Dayal. Meanwhile, Abhay confesses to his co-worker, Tiesta Sen (Neha Dhupia) his love for her as well as his identity of the "Ungli" gang.

Exposing a dirty racquet of money makers in the widely distributed Mumbai police force with a simple chemical trick involving sulphur sprayed overprinted notes that would leave a lasting black impression on the officer's tongue via saliva, Kaale regains duty and is promoted to the post of Commissioner, getting Dayal and Anshuman arrested. Later, Kaale reassures the gang that the city won't need another as long as everything is under control.