Aadhi is the remake of Telugu movie Atanokkade. Aadhi (Vijay) who lives with his foster parents (Manivannan & Seetha) in New Delhi. He takes up a course in a Chennai college against his parents wishes, while he is actually on mission to eliminate the people behind the murder of his blood family.
Similarly Anjali (Trisha) who is studying in the same college has her own agenda to seek revenge on her parents killers, and she is assisted by her uncle (Nassar). Soon Aadhi falls in love with Anjali, as she brings back memories of his childhood sweetheart and cousin who loved to dance in the rain.
In a shocking flashback, it is revealed that Anjali and Aadhi were from the same family. Aathi's biological father (Prakash Raj) who was an honest cop who arrested one of the henchmen of a local gangster, RDX (Sai Kumar). Only Anjali, her uncle and Aadhi survived the blast that annihilated their family.
Together, they combine forces to get revenge on RDX. The climax shows a battle between Aadhi and RDX, in which Aadhi kills RDX with some emotional moments.