A group of peoples are shown falling dead due to the addiction on drugs in Bhavani, one of the place in Erode District. One of the child named Pragalya's death impacts the public very badly.
The police department is pressurized by the government to form an undercover investigation to find about the person who had been involved in the business of drugs in the Erode district.
The police department appoints John William David, a police officer from Chennai to investigate the case. David recalls his life before 2 years when he was posted as ACP of Chennai.
He was a honest police officer who was in-charge to eliminate an important criminal named Rajiv Reddy who was escaping the law in all ways.
His mentor and godfather JCP Rathinavel gives him an unofficial charge to encounter Reddy. John manages to kill him but in the process loses his wife Dhivya and child Esther.
But, still continued his duty despite the loss of his family. John forms a secret team to investigate about the drugs that the childrens had consumed.
Co-incidentally, John's close friend and Rathinavel's son Harsha Vardhan has come to Erode for joining as an NCC master in SVN school. After meeting John, they both stays in the same house.
In a parallel incidents, One day, Harsha watches a school girl trying to intake a drug and he catches her to confront about the drugs.
She tells him that a seller in the bus stop gave her for 100 Rs. After throwing the drugs, he informs the SP and asks him to send a special force to a secret hideout.
This is witnessed by a school teacher who was class teacher for Harsha when he was a student.
But, Harsha explains her about the reason for him being an undercover officer. His father Raghavan, who was a rich businessman was a respected men in Veeralpatti, Pollachi.
But, some jealousy peoples and his father's assistants had killed him for his position.
However, he had escaped and got adopted by his father's brother Rathinavel who was also a police officer like Harsha.
He trained him hard and also posed so many challenges in his life to test his efficiency.
After overcoming all these obstacles, he joins IPS training and again a test is given to Harsha to test his efficiency. But, now it is a difficult competition for him.
As he has to face challenges as an undercover officer. His teacher motivates him to fight against injustice.
David also learns that Harsha is a police officer and his girlfriend Shweta also supports in his undercover mission. When David, Harsha and his team goes to the bus stop, they discovers a paper.
They realises that the criminal has escaped the place.
Later, John and Harsha collects the forensic reports of the dead children and gets shocked after seeing into it.
After the children had consumed the drugs they will be infected by an unknown virus and when it is consumed more they will die.
Harsha recollects the drugs that he catches from a girl in the school and realises that it was sold by a most wanted criminal.
They arrests one of the drug sellers in Erode luckily and realises that a most wanted criminal in Anthiyur had been mastermind behind the plan.
Vetrimaaran is the one behind this plan who wants to destroy India through Bio-war after being bribed by some Chinese peoples.
Harsha and William kills the seller after learning that Vetrimaaran is seeking hideout in Lakshadweep island.
With Kerala and Tamil nadu police teams, Harsha goes to Lakshadweep as a 12 days trip and they surrounds Vetri's hideout.
However, Vetri escapes in a ship while Harsha and William destroys the whole Island and the virus carrying drug with their teams.
Vetrimaaran lands in Erode and kidnaps Shwetha. He threatens Harsha to come for Anthiyur reserved forest areas if he wants Shwetha alive.
After a long ensuing fight, Harsha attacks Vetri fatally and also explains him about care for the nation and impact of betrayal.
Vetrimaaran succumbs after realising his mistakes and faults due to the injuries.
Later, Harsha and John attends a press meet and leaves a message that it is their responsibility to prevent these dangerous crimes which spoils the life of children's,
the need for future generation.
Harsha's foster father again gives him yet an another investigation but, now it is an official investigation implying that Harsha is ready for fighting another war with criminals.
He goes with John David and his wife Shwetha to Tirunelveli, where he has to handle the case as per planned.
While heading to Tirunelveli, David asks Harsha to tell more about his father Raghavan for which he replies that he is not his father but,
indeed he was his maternal uncle killed in an riots before 5 years when he was a police officer to control the riots.
He had framed up the story to the teacher in-order to get their support for destroying these dangerous business.
John David then,
praises him to be an Intelligent cop in framing the stories in order to nab these dangerous criminals in the society and asks him to continue this trick for getting support from
the common peoples.