I want to decipher the creators intent to see if there was any thought process in the entire story line. If you are worried about SPOILERS, there is none. In fact, I cannot think of any SPOILER to write - there is no piece of information given before hand will make the movie any better/worse to watch.
1) Ravi (Vijay) is studying 12th standard (for the fourth time) and wants to become a super cop called "Dhevanath". Following the supercop's footsteps, He drives an auto to pay a tuition fees and lives in a hostel actively , flirting with Suseela (Anushka). Occasionally, he does a remotely "benevolent" act, like opening up windows in class rooms, clearing traffic, but does not let you give credit for him by backing the act with a lengthy dialogue. The whole pattern was vaguely familiar from "Sorry Shaktiman".
2) There are a whole bunch of villains, who do bad things. Ravi starts a fight with the villains mainly to rescue his class mate. The "vettai" (hunt) starts at that time and becomes a full fledge war.
3) The war is much like a turn-by-turn game but without any strategy. Both teams are not capable of looking beyond the next step. It is very similar to chess, because nobody can kill Vijay(I was secretly hoping someone will). Some random villan will be hit/killed by Vijay's plan. Everything else is pretty much uninteresting pawn cancellations. To
make it more boring, there are new villans who are also killed/threatened.
4) Ravi hits Chella. Chella calls the cop (Kattabomman) to arrest Ravi and take him for Encounter under the name of a different popular bomb villan. The good-guy-"pretending"-tobe-bad-guy-due-to-no-[eyes-or-family] Dhevanath sends people to rescue Ravi from encouter by making him do an apocalypto jump. Ravi steals Kattabomman's gun and does the real encounter instead of the fake one there by making the police immune to his presence for the rest of the movie.
5) Kattabomman(the bad cop) losing his second wife Janu for the hairy guy decides not to be a villan and helps Vijay proceed with his next grand strategy, which is drive an auto straight to the villans place (If its that easy why didnt he do it before? oops - sorry its a climax fight.). Due to Kattabomman's insult, the villan decides to enter politics and so Ravi and his friends hate him even more.
6) No one exactly happens in the climax gun shot moment can never be truly understood because its basically few people dancing with guns and aruvas; the villan dies at the end, killed by the blind supercop with voice directions from Ravi.
I had a few laughs at step 1 but was waiting for it be done with when the vettai started. If you watch random youtube videos, with same actors in it you can probably make similar causal analysis and derive your own story which is more solid than this one.
If you are heavily drunk or if you are less than 6 years old, you will probably find this movie very good.
Vettaikaran = "Disgrace to humanity"