SP Diana Joseph (Tabu) captures members of the Sikka Gang and confiscates a haul of cocaine worth Rs 1,000 Crores. An undercover officer Abbas Ali (Tarun Gahlot ) known as Raunak, has joined Ashwathama (Deepak Dobriyal) (known as Ashu) who is co-leader of the Sikka Gang. Raunak gives information about Ashu to Diana.Ashu seeks help from corrupt NCB officer Devraj Subramaniam (Gajraj Rao) who instructs another corrupt officer Deep Singh (Lokesh Mittal) to add Rohypnol to drinks made for police officers at the farewell party of IG Jayant Malik (Kiran Kumar). Devraj has agreed to help Ashu recover the cocaine in exchange for a share of Rs 50 Crores. Devraj tells Ashu that there is a traitor in his gang and tells him that Diana is the officer after the Sikka gang. Ashu swears vengeance. Diana does not partake but everyone else falls unconscious. Diana knows that the Sikka gang will want to recover the drugs. Diana has stored the drugs at Laalganj police station. She doesn't know that she has Ashu's brother Nithari in her custody as nobody has ever seen him. Laalganj is a British era jail made of solid stone and has a bunker in the basement.A prisoner named Bholaa (Ajay Devgn) has been released from prison, but was arrested by an officer on his way to the town for his arrogance. The officer had brought Bholaa to the party, with him handcuffed in the back of his jeep. After the entire force passed out, Bholaa was the only one Diana could turn to for help. Joseph tries to convince him to drive a truck taking the sedated officers to the hospital then on to Laalganj police station. Although he is reluctant at first (he was on his way to meet his daughter after spending 10 years in jail), he agrees when Diana says that he is condemning many other daughters by abandoning their fathers.Meanwhile, Ashu hires a bounty hunter on Joseph and the rest of her police force. As Joseph, Bholaa and sidekick Kadchi (Amir Khan) drive they are attacked by various gangs. The mole Deep Singh, who has hidden with the sedated officers, provides them with the location updates. Bholaa reveals his fighting powers and kills all the goons. Ashu also sends his gang to attack the police station and to free his brother Nithari (Vineet Kumar), who was caught with the cocaine. A new inspector, Angad Yadav (Sanjay Mishra), who was recently transferred to Laalganj, gets assigned by Joseph to defend the police station. Bholaa cannot understand why he is involved in this fight, but Diana continues to remind him his civic and national duty. She promises to unite him with his daughter. Bholaa wants a room for his daughter and an admission in a good school.When Ashu arrives with his gang, they try to breach the police station which is barricaded by Yadav and some students who happened to be at the station at that time. Joseph is nearly tricked into ordering the release of the prisoners (she offers a deal to release the prisoners in exchange for Ashu not killing anyone in the station), but she realizes that it was a trap set by Nithari who was in the lock up. Nithari planned to kill everybody after being released.Ashu manages to get inside but Yadav and the students manage to arrest him. The student Chetan (Chetan Sharma) gets strangled to death by Ashu's gang with a lasso through a window and Yadav, fuming with rage, kills Ashu. Joseph contacts medics to provide an emergency ambulance at a temple of Lord Shiva. As they wait, Bholaa narrates his past to Kadchi: he was a notorious gangster in Uttar Pradesh and fell in love with a doctor named Swara (Amala Paul), who reciprocated his love after he saved her from being sexually assaulted.Before their marriage, Bholaa gave up his gangster life, but Swara was killed by a ruthless gang leader known as Chomu (Abhishek Bachchan). Before dying, Swara gave birth to their daughter, Jyoti (Hirva Trivedi) but Bholaa got separated from her after receiving a long-term prison sentence. Joseph shares her story about how she lost her unborn child when she was pregnant. An ambulance finally arrives and takes the sedated officers to hospital, then Ashu's big henchman Bhoora (Arpit Ranka) also turns up. Before Bholaa is able to fight, Deep Singh stabs him, and he is brutally injured. While Joseph and Kadchi are taken away, Abbas is killed when he is discovered as the mole. Bholaa later regains consciousness and kills the whole gang all by himself, including Deep Singh, using the Trident of Lord Shiva. After this he chases after Bhoora, killing him and rescuing Joseph.After driving all night, Bholaa, Kadchi and Diana arrive in Laalganj police station using a secret passage and help the students along with Yadav to escape safely. Joseph burns the cocaine and after Ashu's reinforced gang finally breaches station, Bholaa destroys them all using a M134 Minigun.Shortly after, Nithari dies of shock after learning about Bholaa, and Devraj Subramaniam shoots himself after knowing that Bholaa was behind everything. Bholaa is reunited with his daughter Jyoti and they drive off happily in the truck with Kadchi and a puppy. In a mid-credits scene, Chomu Singh learns about Bholaa's release and decides to destroy him.