Director: Prakash Jha
The film begins with Senior Superintendent of Police (SSP) IPS Amit Kumar (Ajay Devgn) taking charge of the fictitious Tejpur District (West Champaran) in [Bihar]. The area is notorious for its crime rate, with Tezpur Police under the control of the local don Sadhu Yadav (Mohan Joshi) and his son Sundar Yadav (Yashpal Sharma). While travelling to the headquarters on the first day of his duty, Amit’s car breaks down and he uses this as an opportunity to inspect the area. While touring the area, Amit observes a systemic rot in the administration of the place what with the professional laxity among police officials, crumbling infrastructure, outdated weaponry, lack of basic facilities like stationery and transportation and the dependence of the officials on corrupt local contractors for the same. Amit also finds that most of his subordinates are on the payroll of Sadhu Yadav and exchange favors. Amit tries to instill honesty and courage in his subordinates, but in vain.
Inspector Bacha Yadav (Mukesh Tiwari), one of Amit Kumar’s subordinates, who is a stooge of Sadhu Yadav visits his hideout and sees an infamous local goon Nunwa taking shelter there. Nunwa is found to have been underground all the while, after killing an officer in Bachcha Yadav’s department, owing to a heated argument between them. Fearing that arresting him would open the lid on the nexus between Nunwa and the Tezpur Police, he kills Nunwa at Sadhu’s behest and misleads the police and public into believing that he was killed in an encounter. Sadhu Yadav’s purpose behind getting Nunwa bumped off is that he’s trying to kill two birds with one stone, where killing Nunwa would eliminate the danger of the detection of his links with himself and the police force as also would help him to ingratiate himself with Amit Kumar. However, Amit sees through Sadhu’s designs and chides Bacha Yadav for his cowardly act. He also warns Bacha that people like Sadhu Yadav are opportunists and fraternization with the latter merely due to belonging to his caste won’t help him. He points out that Sadhu sold off Nunwa when he outlived his usefulness even when he sought refuge with him, and would do the same to Bacha some day. Amit puts Bacha off duty temporarily as a punishment and also tries to keep him away from Sadhu Yadav and Sundar Yadav. Anxious that he would be transferred from Tezpur, Bacha Yadav, seeking the help of Sadhu Yadav, visits his home, where he finds out that he is being ditched by Sadhu and vows to settle score with them. Meanwhile, Sundar manhandles a Public Works Department engineer for not heeding to his word during a tendering process. Amit takes notice of the incident and also finds that a girl is missing from her home after being kidnapped by Sundar. Sensing an opportunity, Bacha Yadav urges Amit to give him one more chance, who obliges him. Bacha Yadav tricks Sundar into a factory where Amit and his men are waiting and after a brief scuffle, Sundar is arrested and produced in a local court, where the judge acquits Sundar on the account of lack of evidence against him.
Sadhu Yadav’s men then try to vandalise the shop of a local pan vendor after he testified against Sundar, before being arrested and jailed in the police station. There, a fight arises between the accused and Bacha Yadav and his colleagues. It reaches an extreme point with Bacha Yadav and his colleagues piercing the eyes of the accused and pouring acid, referred locally as “Gangaajal”, into their eyes. The incident raises a hue and cry in the local media, which accuses Police of vigilante justice. Angered by the incident, Amit Kumar orders his men involved to give their confessions in writing. Taking macabre inspiration from the incident, emboldened police officials in the vicinity conduct the same “experiment” on hardened criminals languishing in their jails. This creates an acute fear psychosis throughout Tejpur, with crime rates considerably lowering. The violent nature of this vigilantism finds support in the harrowed public of Tejpur which harbors simmering anger against the Yadavs owing to their bullyism and the general circumstances of deprivation in the town. “Gangaajal” becomes an instrument of extrajudicial “instant justice”, to be meted out to the perpetrators of serious crimes. Any voice of dissent with regard to the practice is swiftly and violently shut down. While all officers, except Bacha Yadav, deny their involvement in the incident, Bacha Yadav writes his confession in a letter and submits it to Amit. When Bacha Yadav reaches his home, he finds his son and wife taken hostage by Sundar Yadav who, after a brief struggle, kills Bacha Yadav by shooting in his eyes. Enraged by the incident, Amit Kumar burns the confession letter of Bacha Yadav and issues a search warrant for Sundar and warns Sadhu Yadav to tell Sundar to surrender himself. Sadhu Yadav applies for an anticipatory bail for Sundar but before Sundar is produced in the court, he is arrested and is taken to jail. This time, the court rejects the bail application and orders the Police to keep Sundar in a 10-day custody.
However, Sadhu Yadav influences local home minister and the Deputy Inspector General of Police (DIG) (Mohan Agashe) of the area, Verma, to release his son which Amit Kumar stubbornly refuses to do. As a result, Amit is sent on an emergency leave. Meanwhile, an enquiry commission is set up to investigate the gross human rights violations under Amit Kumar’s jurisdiction. While his subordinates including Tiwari, Khan, Pandey, deny involvement and plead their innocence, Amit unconditionally accepts responsibility for the incidents on moral grounds despite receiving overwhelming support from the populace of Tejpur. This perplexes his subordinates who find themselves helpless in the face of this situation. After being released, Sundar disrupts the marriage of the girl who he kidnapped earlier and kills her mother in the process. Unable to bear the loss of her mother and the torture at the hands of Sundar, she kills herself in the presence of Amit. Amit detains both Sadhu and Sundar and tries to take them to the police station. However, an enraged mob of locals stops Amit and demands that both be killed then and there itself by subjecting them to the same practice of gouging their eyes out and pouring “Gangaajal”, before being convinced by Amit that anarchy can never be the answer to oppression and would only bring about social and moral decadence, which in turn would further engender authoritarianism. He insists that they would be tried as per the law. However, on the way to the police station, both Sadhu and Sundar, probably paranoid about their fate in prison, make a last-ditch attempt to escape by overpowering the guards and snatching their weapons . Amit then catches up with them as they hold a family hostage to ward him off. A brief fight takes place between them and the film ends with both Sundar and Sadhu getting killed by falling accidentally on the chisels of a plough, which incidentally pierce through their eyes. SSP Amit just walks away.