Aegan's story is based around Shiva (Ajith Kumar), a CB-CID officer, and his efforts to foil the terrorist John Chinnappa (Suman). Shiva is simultaneously attempting to mend relations with his father's estranged first wife and his half-brother Narain (Navdeep). Complications ensue.

John is a scientist who had created tablets by operating on human guinea pigs. His ploys have always been controversial but inconclusive due to lack of witnesses. However, an ex-gang member General Ram Prasad (Devan) became a police approver and is on the verge of revealing John's ploys to the police. However, he is on the run to avoid charges. The case falls to Commissioner Karthikeyan (Nassar), Shiva's father, who assigns his son to go and help solve the mission.