One of the best movies of all times.
The core of the movie is based on the historical story of Vikramadithyan & Vethalam. Vikramadithyan captures the Vethalam and carries it on his shoulders. While walking, Vethalam recites a story and at the end of the story, it asks a question. If Vikramathithyan answers, it will fly back to the place from where he caught it (a tree) and if he doesn't, Vikramathithyan's head will burst into 1000 pieces
Similar to this story, Madhavan (Vikram) plays the lead role of Police Inspector and Vijay Sethupathi (Vedha) plays the role of a goon. Vikram and his team will carry out an encounter operation in which Vikram's younger brother will get killed. While Vikram & his team plan to find out Vedha's hideout and neutralize him, Vedha walks into the Police headquarters with a gun and turns himself to the Police.
Because he surrendered, the Police cannot carry out an encounter operation. So everyone in the department will speak with Vedha to make him speak - on his plan, why he surrendered, etc... But when Vikram comes to speak with Vedha, then Vedha tells him a story and asks him a question.
At first, the questions asked does not have anything to do with what is going on in the movie but as they keep meeting, Vedha recites different stories which happened at different points in time in his life, and the questions open up a lot of information to Vikram, which helps him solve the case on hand.
Verdict: Amazing movie, must watch. The screenplay is amazing and not even for a minute, you would feel bored / left out. The movie background keeps lingering in your head for days. Vijay Sethupathi's acting is amazing, especially when he asks, "Oru kadha solla taa Sir"