A Turkish Interpol officer, Aslan Yilmaz investigates the assassinations of Chief Minister of Odisha, Mayor of France and Prince of Scotland, where he, along with a young Tamil criminologist Judith Samson, deduce that Cobra, a flawless assassin is the mastermind behind the assassinations. The duo learn that Cobra assassinates his targets using mathematical skills, leading them to believe that he is a professor of mathematics.Meanwhile, Mathiyazhagan "Mathi" is a mathematics professor, who is actually Cobra, receives his next assignment from his mentor and senior journalist in Kolkata, Nellaiappan. He is to kill the Russia's defence minister, Dmitri Yugolsav. He travels to Russia and manages to successfully assassinate him and escape, despite tight security from the Interpol. Before Yugolsav was killed, Aslan and his team watches a telecasted conversation between Nellaiappan and Nawab, who works at a company named Rishi Corporation, where he concludes that the victims are connected to the company's owner Rajeev Rishi, a psychotic and sadistic business magnate, who inherited the company from his father. After his engagement to his criminologist girlfriend and Judith's teacher, Bhavana Menon, Mathi learns that Nellaiappan has been kidnapped and learns that someone has targeting him from the beginning of his assignments.After a clue from Sudoku, Mathi receives a call from the person, who is Mathi's doppelganger, where he challenges Mathi to save himself from him. In a turns of events, it is revealed that the person who is referred to as Mathi is actually Kathir, Mathi's schizophrenic long-lost twin brother and the person who challenged Kathir is the real Mathi. Rishi sends men to capture Mathi, but Kathir manages to kill them. Mathi had been holding a grudge against Kathir, as he was responsible for the death of his girlfriend, Jennifer Rosario, who was the daughter of the Kolkata city commissioner Rosario. Mathi learnt about Kathir's identity as Cobra and planned to seek vengeance for Jennifer's death, where he reveals that he was the one who was sending clues about the assassinations to the Interpol.Mathi hands over Kathir to Aslan, where Anand Subramaniam, the investigating officer and Rishi's mole, takes Kathir's help to capture Mathi. Kathir brings them to Mathi's hideout which is an under-constructed mall. Rishi arrives and a fight ensues between the gang and Kathir, where he successfully manages to subdue them. Mathi confronts Kathir about Jennifer's death. Kathir reveals that he had arranged for Mathi and Jennifer to leave for Bangladesh, but her father and relatives followed and killed her. After clearing the misunderstanding, Kathir reveals that he had killed Jennifer's relatives and locks Mathi in a room. Kathir shoots Rishi and his men, but gets shot in the process and dies, thus leaving Mathi and Bhavana devastated.