Parthiban "Parthi" is an animal rescuer and a cafe owner in Theog, living happily with his wife, Sathya, and two children, Siddharth "Siddhu" and Mathi "Chintu". One day, Parthi's friend, Joshy Andrews, a forest ranger, calls him to help tame a spotted hyena on the loose. With Siddhu's help, Parthi manages to tranquilise the hyena and save the townsfolk. He purposefully avoids public attention over this incident and adopts the hyena after it calms down.
One night, Parthi and Chintu are at the cafe when a dangerous gangster named Shanmugham and his men arrive to rob the café. Parthi tries to appease them by giving them money, but one of the gang members makes a move on a female employee. Enraged, Parthi beats up all of them. When one of them attempts to kill Chintu, Parthi guns all of them down without hesitation, but later has an emotional breakdown. Initially arrested, Parthi is released for having committed the murders in self-defense, but his photograph appears in newspapers all over India. One such image is seen by a notorious gangster named Harold Das in Telangana, who informs his elder brother, Antony Das about him.
Meanwhile, Shanmugham's relatives attempt to kill Parthi and his family, prompting him to request a high-ranking, armed police officer from Tamil Nadu to be sent to his house for protection. Parthi's request is granted as Napoleon, having been promoted recently following his heroics in Trichy,[a] is assigned to protect his family. On meeting Parthi, Antony insists that Parthi is his son, Leo Das, who was assumed to be dead, but Parthi vehemently denies this. Antony threatens him to accept his identity and surrender or face the consequences. Antony meets Sathya and tells her that Leo is a mass murderer, prompting her to dig into Parthi's past. At the same time, Joshy starts digging into Leo's past and finds out about his friend, Irudhayaraj D'Souza, who was arrested and is to be hanged in three days. On meeting with Irudhayaraj, Joshy learns about Leo's past.
In 1999, Antony established a tobacco factory called Das & Co. Harold returned to India from Canada and started smuggling drugs, using the factory as a front as their tobacco products did not take off. Antony's twin children, Leo and Elisa Das, did the dirty work for them to run the business smoothly. Being a strong believer in the occult, Antony tried to sacrifice Elisa based on his astrologer's advice, as this would have allowed their tobacco products to take off. Enraged, Leo set fire to all of Harold's drugs, but Harold managed to kill Elisa and Antony shot Leo, who was since then presumed to be dead.
On hearing this, Joshy is convinced that Parthi is not Leo, while Sathya also gets definitive proof of the same. Meanwhile, Antony kidnaps Siddhu and tells him that he will sacrifice Siddhu as he could not sacrifice Elisa with his own hands. Parthi and Napoleon give chase to Antony and his men, and Parthi eventually catches up with them. He finishes off Antony and his men but does not find Siddhu. Harold learns about Antony's death and calls Parthi to bring Antony's body in return for Siddhu. As Parthi goes to Harold's lair, Harold reveals that he has sent men to kill Sathya and Chintu. However, Napoleon, Joshy, and the hyena finish off all the men. Harold's men attack Parthi at their lair, but he manages to fend them off. As Harold and Parthi engage in a fistfight, Parthi grabs a gun and holds Harold at gunpoint.
At this point, Harold admits that Parthi is not Leo and states that he and his family can walk away freely. However, Parthi starts laughing and finally admits that he is Leo before gunning down Harold and blasting the entire Das & Co. factory. Leo states that he has done nothing good in his past and anyone who knows his history must not remain alive.
In an epilogue, as peace returns to Parthi's family, he gets a phone call. The caller[b] reveals that he knows Parthi is Leo and tells him that destroying only his family's factory was not enough as drugs are rampant all over India. The caller also says that he knows Parthi recognises his identity, as Parthi sighs in exasperation.