Rani, the daughter of former Chennai police officer SP Arokiya Raj, tells her father from a telephone booth that she will return to Madurai soon. As she steps away, an acquaintance approaches and she does not come home. The next morning, Arokiya Raj finds Rani’s index finger left at his door. He contacts DCP Raghavan, Kamal Haasan, a former Chennai colleague, to help with the investigation.
Raghavan discovers Rani's body within 12 hours, buried on the outskirts of Madurai. The autopsy reveals the killer slit Rani's throat with a scalpel and bisected her body with an axe, signaling a medical background. With little solid evidence, the case remains open. Six months later, Arokiya Raj, Prakash Raj, and his wife Chithra, following the trauma of losing their only daughter, move to New Jersey.
Three months later, Raghavan learns that both Arokiya Raj and Chithra have been murdered in New York. Collaborating with the NYPD, Raghavan travels to New York. On the flight, Raghavan recollects memories of his late wife Kayalvizhi, Kamalinee Mukherjee, who was abducted by a local gang and fell to her death. Upon arriving, Raghavan stays at a hotel in Downtown New York and keeps his superiors in Chennai updated on the investigation. There, he meets Aradhana, Jyothika, an NRI who is going through a rough patch; concerned for her safety, he breaks into her room and saves her when she attempts suicide by asphyxiation. Aradhana reveals that Arun, her violent husband, is filing for divorce after cheating on her. Later, Raghavan and Lev Gorn discover a connection between Rani's murder and a two-year-old unsolved disappearance of Chandana, a 23-year-old Indian American girl whose finger was possibly found in her boyfriend Hitesh's car.
Raghavan's instincts lead them to Chandana's body in a restricted suburban area, found alongside three other American women who were murdered in a similar pattern. Narrowing down suspects through flight records, their attention turns to two Indian doctors who studied at Brooklyn Medical University: Amudhan Sukumaran, Daniel Balaji, and Ilamaran Aanandhan, Salim Baig, who are secretly involved in the killings. They murder their former professor Veronica, along with two NYPD officers in the same area, where Raghavan had set them under surveillance. Raghavan and Anderson (the NYPD counterpart) visit Amudhan's and Ilamaran's apartment only to find it unoccupied. A break-in reveals pictures of the victims and the murder weapons, confirming that Amudhan and Ilamaran are the serial killers.
Before backup can arrive, Ilamaran arrives unannounced and kills Anderson, while Raghavan fights him and eventually knocks him unconscious. Amudhan stabs Raghavan with a scalpel to buy time. To understand Amudhan's motive, Raghavan asks why he killed Arokiya Raj, his family, Chandana, and the other women. Amudhan explains that they had a habit of killing from childhood, starting with pushing a classmate from a train at 13 and murdering their school teacher at 17; they stopped after entering MBBS at Rani's college. He claims their violent urges resurfaced when Rani provoked him, and two days later Arokiya Raj assaulted the duo outside a theater, after which they were detained and tortured by a local inspector who neglected proper interrogation.
The pair flee to New York to pursue further studies in surgery, abducting and killing local young women who looked down on or disrespected them. While on a holiday trip back to India, they met and killed Rani, then returned to the United States and followed Arokiya Raj and Chithra to New York to finish them off. Believing Raghavan to be dead from his injuries, they set their apartment on fire and escaped to Mumbai, only to be halted by the Mumbai police and eventually reach Chennai. Raghavan survives with severe injuries and is cared for by Aradhana, strengthening their bond. Four weeks later, they return to Chennai together. Aradhana reveals that she has a daughter living with her parents in Chennai, and she is not ready for another relationship, choosing instead to focus on motherhood. Raghavan announces a statewide hunt for the killers, and the dean of their medical college revokes their degrees, marking the start of a violent manhunt.
As Aradhana and Raghavan navigate the danger, Amudhan abducts Aradhana while Ilamaran attempts to infiltrate Raghavan's home. When the police arrive, Ilamaran tries to flee but is captured; the two killers are revealed to be bisexual and in a hidden relationship. Raghavan confronts Amudhan, and in a final confrontation, he kills both Amudhan and Ilamaran, avenging the deaths of Anderson, Arokiyaraj, Rani, and Chitra. He then locates Aradhana, revives her, and after a few months, Raghavan and Aradhana marry, beginning a new chapter after a long and harrowing ordeal.
