In a quiet corner of Ooty, a routine transport spill becomes a deadly catalyst: a container of poisonous liquid cracks open at a chemical laboratory, a stray dog laps it up, and the animal’s aggression spirals into a deadly outbreak. The virus passes from bite to bite, turning those infected into zombies within hours and setting off a chain reaction of fear, chaos, and desperate attempts to find a cure.
Back to the present, Karthik is a careful, risk-averse traffic police sub-inspector in Ooty who keeps danger at bay while shouldering the care of his younger sister Vidya. The two are orphans who live with Chinnamalai, a loyal traffic constable and close friend who helps keep them safe in a city already on edge. Karthik harbors a quiet, unspoken love for Renuka, commonly known as Renu, a compassionate cardiologist who is soon to marry a visiting NRI named Naveen, Amit Bhargav. This triangle of affection unfolds against the backdrop of a city collapsing under the shadow of the undead.
A reckless moment changes everything: Karthik inadvertently crosses minister Gurumoorthy by permitting an auto carrying pregnant women to pass through his route, drawing the minister’s ire and triggering a political clash that will come back to haunt him. The following morning, Vidya disappears, and Karthik is attacked by zombies while the city erupts into confusion and panic. The police are ordered to shoot anyone who has turned, turning the streets of Ooty into a fog of gunfire and fear as Karthik searches for his sister, poster after poster plastered on walls in a desperate bid to locate Vidya.
His quest leads him to a house where a vaccine effort is underway, a team led by the Chief doctor Dharan. Among the group are Renu and a handful of doctors who are racing against time to counter the plague. At a key moment, Karthik discovers Vidya inside a building owned by her captors, guarded by the minister’s zombified henchmen, and learns that the zombies have one unusual weakness: they are allergic to water. The scene shifts quickly to a tense confrontation at Renu’s home, where Minister Gurumoorthy’s machinations reveal that Vidya has been kidnapped as part of a personal vendetta against Karthik.
With Vidya’s safety uncertain, the team chooses to head for Coimbatore, carrying the necessary medical gear in hopes of developing a cure that will halt the spread. Dharan has already been scratched by a zombie, a secret he withholds in a bid to protect the mission, while the infection quietly gains ground back home. As they travel toward Mettuplayam, the virus has already begun to circle the neighboring city, and crowds grow restless as zombies converge on the police vehicle, forcing Karthik to maneuver through danger with seconds to spare.
A fateful misstep by Gurumoorthy stirs a fresh wave of undead, drawing more attackers and forcing the group to take shelter in a mall opposite a hospital. Inside the hospital, Naveen waits, searching for the vaccine, while Shri, a terrified mall security guard, hides from the chaos. The doctor's team leads Dharan to safety, but his own awakening as a zombie becomes imminent when he is bitten, and Vidya, though badly hurt, seems to escape infection for the moment thanks to Kamal’s medical insight that she may possess the antibodies and immunity needed to unlock a cure.
Karthik concocts a plan to exploit the mall’s water supply, using pressurized water from the mall’s fire truck to subdue and repel the advancing zombies long enough to transport the group to the hospital. In a race against time, he escorts everyone except Renu to safety, returning later in a bid to rescue her. The rescue mission goes awry when Karthik is bitten while shielding Renu, his humanity fighting the slow, inevitable transformation. He urges Renu to shoot him before the infection fully takes hold, even as she struggles to understand his selfless motivation and his deep love for her.
Renu’s resolve finally crystallizes, and she shoots Karthik, severing a potential tragedy and buying a chance for the cure to reach the city. The medical team recovers the crucial antidote and mobilizes to deploy it, finally confronting the terrifying reality of the outbreak. In a heartbreaking and heroic turn, Karthik, now a zombie, is seen on the top of a bus bound for Chennai, a chilling implication that Renu’s shot may not have fully ended his life and that his fate—and the story—will continue in a possible sequel.
The film closes on a note of uneasy hope: the antidote exists and the doctors move to deploy it, but the price has been high, and the line between life and death has never felt thinner. The last image leaves audiences with a sense of unfinished business, a setup that promises more to come as this virus tests the limits of love, loyalty, and the resilience of a city trying to recover from an apocalypse that began in a hidden, toxic spill.
