An ambulance driver, a broker, a hospital worker, and a surgeon are abducted at dawn, which is traced to Dr. Maaran, a doctor from Chennai known for providing treatment to all at just ₹5. Maaran is arrested and interrogated by Ratnavel “Randy”, a police officer who is assigned the case. Maaran explains his motive for the abductions; the four were responsible for the death of the auto driver’s daughter and subsequent suicide of his wife, Selvi, due to their greed for money and negligence in providing proper healthcare. He gives Randy the locations of his hostages but asserts that he had already killed them simultaneously using contraptions.
Maaran reveals that he is not Maaran but his doppelgänger Vetri, a magician. Vetri was also responsible for the death of Dr. Arjun Zachariah, a corrupt doctor who was killed during a stage performance in Paris two years earlier. Dr. Daniel Arokiaraj, another corrupt doctor and the head of the state’s medical council, had been associated with Arjun who sees Maaran’s inexpensive healthcare as a threat to his flourishing hospital business and decides to kill Maaran using his goons and one-armed henchman Kasi but is saved in the nick of time by Vetri, who knocks Maaran unconscious and swaps places with him, providing clues to the police which led to his arrest. Maaran is rescued, while Vetri, manages to escape from Randy. Later, Maaran confronts Vetri, believing him to be the cause of all his problems. Vadivu, Maaran’s compounder, and also Vetri’s assistant intervenes and explains to Maaran why Vetri is targeting doctors indulging in corrupt medical practices in general and Daniel and Arjun in particular.
Maaran is the elder son of Vetrimaaran, a village wrestler and chieftain from the 1970s and Aishwarya “Aishu”. Vetrimaaran, being referred to as “Thalapathy” by his villagers due to his altruistic nature, decides to build a temple in his area and holds a large scale event with a festive mode. However, a fire breaks out, injuring many and killing two children due to lack of mobility. By the advice of Aishu, Vetrimaaran had established a hospital with the help of a younger Daniel and Arjun in his village Manoor in Madurai district and made chief doctors, while Vetrimaaran managed the hospital. However, it soon turned out that Daniel and Arjun were money-minded misanthropists and performed a Caesarean section on Aishu when she was in labor with her second child, to extract more money from Vetrimaaran, even though she could deliver the child normally. Aishu lost a lot of blood during the operation, and along with an overdose of anesthesia she dies while the child was declared stillborn. When Vetrimaaran found out how Aishu had died, he went to confront Daniel, but was attacked by empty bottles. Vetrimaaran fights but in the end gets stabbed to death by Kasi, but just before he died, he amputated Kasi’s arm and placed an unconscious Maaran (who had been struck on the head with a glass bottle) safely on a Chennai-bound lorry. Daniel admits that he was the one who set fire to the temple and ruthlessly killed those children so he could set up the hospital just to rob and kill everyone; thus Vetrimaaran swears that one day Daniel will pay for his misdeeds. Maaran lost his memory and was unable to recollect anything that happened before passing out due to the impact of the bottle on his head. After killing Vetrimaaran, Daniel and Arjun embezzled money in medical service to consolidate their dictatorship over the years, while creating a massive genocide from beyond.
Meanwhile, Vetrimaaran’s second child was not stillborn; he miraculously survived and this child was Vetri and Vadivu, their paternal uncle (Vadivu is the younger brother of Vetrimaaran) took care of him. Both were adopted by a famous magician Salim Ghosh, and it was from him that Vetri learned all his magic tricks. Vadivu explains that by seeing both Vetri and Maaran, it reminded him of the qualities of his brother; Vetri had his anger and sense of justice and Maaran had his sense of selfless service. Upon hearing Vadivu’s story, Maaran reconciles with him and Vetri and takes his place when the police arrive. With Vetri (who is actually Maaran) seemingly in custody, Daniel meets him in prison and expresses his hatred and contempt for all humans and contemplates on misusing medical industry for his personal gains. Meanwhile, Daniel’s nephew Sesha tries to make a deal with Maaran (who is actually Vetri) to shut down his practice. However, when they both learn the truth, Vetri slits Sesha’s hand. Daniel rushes to Vetri’s hideout. Vetri defeats all of Daniel’s henchman and injures Daniel with a glass bottle but just then Kasi crashes a bus into Vetri making him faint. In the truck is an unconscious Maaran who got involved in an accident orchestrated by Daniel. Maaran wakes Vetri up but as Vetri is injured Maaran goes and kills Kasi by himself. Just before Daniel can strike Maaran, he and Vetri team up and kill Daniel.