A gang has kidnapped a girl and several police officers, including Karthik (Sibiraj), who is attempting to rescue her. During a shootout, one man from the gang and a police officer named Arul Das (Raghav Umasrinivasan), who is a good friend of Karthik, are killed, while Karthik gets injured. He is put out of action and suffers from posttraumatic stress disorder.
Subramani (Idoh) is a trained military dog who has the potential to nab culprits and decipher crime scenes. After its owner, an army officer, is shot dead, Subramani is returned to the officer's father in Coimbatore, who is a neighbor of Karthik. The neighbor leaves the town and requests Karthik to provide shelter to Subramani during his absence. Karthik denies the request but provides shelter after seeing Subramani being troubled by the small kids in the neighborhood. Karthik learns about Subramani and becomes good friends with him.
Meanwhile, Karthik's wife Renuka (Arundhati) is abducted by Anbu Das (Balaji Venugopal), the head of the kidnapping ring, and is buried alive inside a coffin. A web camera is attached into the coffin, and the live stream is provided to Karthik. Karthik learns that Renuka can breathe for about six hours. Renuka speaks to Anbu, and with the help of a deaf and dumb teacher, Karthik deciphers what Renuka had conveyed. Suddenly, water trickles into the coffin, and Karthik concludes that it has to be rainwater. He, Subramani, and his cop friend travel to Ooty, the only place in Tamil Nadu where it was raining at the moment.
Anbu had kidnapped Renuka to avenge the death of his brother, who was not the man from his gang, but Arul, who worked as a mole in the police department. Karthik is then hit by a metal rod and is also buried in a coffin. Subramani sniffs out Anbu and his henchmen. While Anbu can escape to a tree house, his henchmen get bitten by Subramani, who saves Karthik by digging a pit. Anbu gets hold of a gun and shoots at Subramani, injuring him fatally, before Karthik manages to outwit and defeat Anbu in a fight. Before dying, Subramani had marked the place where Renuka is buried, and Karthik saved her, while Anbu has been buried alive in the same manner.
Subramani has gotten offspring, and Karthik is given one of the puppies. The movie ends with a scene where Karthik and his new dog, who has been named Chinnamani in Subramani's memory, are being entrusted with investigating a new case.