After busting the consignment of Adaikalam and Anbu by Inspector Bejoy three months earlier,[a] Police Chief Jose summons Amar and his black-ops team to bring justice to a group of masked vigilantes responsible for the deaths of Stephen Raj (following his arrest and subsequent release after being busted for helping Adaikalam and Anbu), ACP Prabhanjan and his foster father Karnan. Amar leads the investigation by digging into Karnan's life as his murder seems out of place because Karnan was an ordinary man, while the other two were higher officials in the NCB.
Amar learns about Karnan's recent addiction to alcohol, drugs and prostitutes and his protectiveness of his infant foster grandson. Amar also finds out about two missing containers of narcotics. Sandhanam, who runs a much bigger drug syndicate than Adaikalam, named Vetti Vagaiyara, is searching for the containers. His cold-blooded smuggler boss 'Rolex', whose identity is unknown, was meant to receive the containers. Amar learns that Rolex would help Sandhanam form his government if the drugs are delivered or Rolex will kill Sandhanam and his family. Amar slowly figures out that all of Karnan's addictions were a ruse to cover up a highly covert operation.
Meanwhile, Veerapandian is a PWD officer who along with a contractor named Rudra Prathap plan to bring the drug containers to Sandhanam. However, the masked vigilantes arrive and kill Veerapandian at a theatre. Amar and his team capture one of the vigilantes, revealed to be Bejoy. Bejoy reveals his family was killed for his role in leading the earlier drug bust, leading him to join the vigilantes. Amar and his team realise Rudra Prathap is the next target, where they sneak into Rudra Prathap's daughter's wedding ceremony. Rudra Prathap invites Sandhanam for protection. However, the masked men and their leader arrive at Rudra Prathap's daughter's wedding and threaten him. The leader drags Rudra Prathap and escapes on a bike, leaving the other members to deal with Sandhanam, but Sandhanam defeats them.
Amar chases the leader down, who is revealed to be Karnan, who faked his death. Karnan kills Rudra Prathap by slitting his throat and escapes the police. Amar discloses to Jose that Karnan is actually Vikram, the former commander of the black ops squad's pilot batch of 1986. After a botched mission, the government hunted and brutally killed all squad members and their families; only Vikram and three other team members survived. Amar also figures that Jose is Sandhanam's mole in the department and is involved in Prabhanjan's death. Amar orchestrates a bomb blast at Sandhanam's house, which destroys his bungalow and drug lab. Jose informs Sandhanam and everyone (except Sandhanam's brother Elango) is evacuated from the blast site in time. Jose reveals Vikram and Amar's identities to Sandhanam
Vikram arrives at the prison and frees Bejoy and his team. Vikram reveals that the reason for actions is not vengeance over Prabhanjan's death, but a mission to bust the drug syndicate in the city. He also admits that Prabhanjan is his own biological son. Sandhanam murders Amar's wife Gayathri and sends his men to attack and kill Vikram's daughter-in-law and grandson at Prabhanjan's house. Vikram rushes to save them, but the gang kills a team member of Vikram's black ops squad and associate Agent Tina, who was disguised as the house help Valiamma. Vikram and his grandson reach Chennai Port, where the hidden containers are stored. Sandhanam learns about the containers' location and attacks Vikram. Vikram mows down Sandhanam's men with a cannon and an M2 Browning, but the remaining members of his black ops squad Uppiliappan and Lawrence die in the scuffle. After a fistfight, Vikram triggers a huge blast at the port that kills Sandhanam and destroys the drug containers.
In Sassoon Docks, Mumbai, Adaikalam and Anbu arrive with their men. They meet up with the gangsters affiliated with Sandhanam for a meeting with Rolex. Adaikalam and Anbu explain Dilli's involvement in the drug ambush and Sandhanam's men reveal Vikram and Amar's involvement in destroying their drug syndicate. It is shown that Amar joined Vikram's gang after Gayathri's funeral to continue the fight against drugs. Anbu informs Rolex that Dilli is currently hiding somewhere in Uttar Pradesh while Sandhanam's men tell him that Vikram's family is in San Francisco. Rolex announces a massive bounty for the execution of Amar, Dilli, and Vikram's team. Unknown to everybody else, Vikram is also present at the meeting and walks away after learning about the bounty placed on Dilli and his team.