Irfan Ahmed, an IIT Madras gold medalist based in Triplicane, Chennai, lives with his friends and his mother, Praveena Begum, a Sub-Inspector of Police. He is in a relationship with Archana Krishnamoorthy, who is doing her Ph.D. in Delhi, and also befriends a junior lawyer, Prarthana Raman. Irfan struggles to land jobs, often failing at interviews, and works part-time at a perfume factory. Frustrated by being questioned about his religious beliefs during interviews, he decides to join the full-time perfume business headed by Perumal and his son, Karthikeyan. He travels the country to source chemicals and, on the return trip from Hyderabad, loses his cellphone.
Struggling with a possible missed flight back to Chennai, he inadvertently threatens the airport officials that he will bomb Hyderabad, which leads to his arrest; he is released and returns to Chennai. A bomb explodes at the airport the next day, killing many people. The following day, his phone is found at the blast site and Irfan is arrested again. He is detained under orders of NIA advisor Ajay Dewan and interrogated by NIA officer Anisha Qureshi and a low-ranking police officer Gunashekhar. Irfan is believed to be the most wanted terrorist, Abu Bakkar Abdullah, and becomes a public villain in the media, subjected to harsh treatment while in custody.
Feeling empathy for him, Prarthana decides to represent him and brings Praveena Begum to visit him, but they are denied. Praveena collapses from an asthma attack due to the humiliation. Irfan is allowed to visit his mother in the hospital, under extreme surveillance, but he escapes from custody and discovers that Praveena Begum has died, leaving him devastated. He escapes the hospital and is approached by Dr. Zazi's son Riyaz, who convinces and motivates him to create a sarin gas to carry out a terrorist attack. Irfan agrees, and the plan is tested on Dr. Zazi when he visits the factory, shocking him as he realizes what is really going on.
Anisha reaches the facility and surrounds Irfan and Riyaz, but is stabbed by Karthikeyan, who is revealed to be the real Abu Bakkar Abdullah. When the bomb is activated, Abu Bakr triggers it and orders his henchman to kill Irfan, but Irfan overpowers the henchman, revealing that he is actually an undercover NIA agent who has waited for years to draw Abu Bakr out of hiding. Archana arrives as an undercover NIA agent and finishes off Riyaz, while Irfan kills Abu Bakr. Gunashekhar and the cops surround the factory under Ajay Dewan’s orders. After getting permission from the Defense Minister, a government drone fires a missile at the factory.
Archana tries to persuade Irfan to leave the factory before it is destroyed, but he stays to stop the activation of the sarin gas. The factory is wiped out by the missile, seemingly killing Irfan. Ajay Dewan is celebrated for preventing the gas attack, and it is revealed that the entire operation was his plan, known to only a few. He had found an officer with a chemical engineering background and named him Irfan Ahmed, erasing the man’s past life. With Archana’s help, Irfan eliminates Abu Bakr’s chemical engineer Ashraf to lure Abu Bakr to India. It is also revealed that Irfan survives the missile strike and continues on another mission, where his real name is revealed to be Faizal Ibrahim Raiz (FIR).
