Ayyadurai(Sarathkumar) has been the local MLA ever since he killed the sitting MLA, who was robbing his constituents off their food. Maadasamy(Napoleon), who belongs to a different caste, has been his right-hand man since those times. Muthupandi's daughter Selvi(Nayanthara) loves Chelladurai(Sarathkumar), Ayyadurai's son but he does not reciprocate her feelings. Karuppusamy(Prakashraj), son of the MLA who was killed, holds hatred for Ayyadurai. He plans to become the MLA by either killing Ayya or driving a wedge into his friendship with Muthupandi, thereby getting the votes of everyone belonging to their caste.

Ayyaa is populated by strong characters but more importantly, Hari allows us to come to know them well by spending time with them. The movie doesn't hurry things along at the expense of character development. For instance, from the first scene where Napoleon saves Sarathkumar's life, the films's focus is on the friendship between Sarath and Napoleon. So we know that the movie's key plot development will be a break in this friendship. But the break doesn't happen until well into the second half. By the time the break happens, we have come to admire Ayyaa's character and the strength of his friendship with Napoleon. So the break is emotionally effective and we genuinely feel sorry for Sarath.

The movie does not focus on the main two characters and their friendship alone though. All the major characters are well-rounded and the relationships between them are also portrayed well and in a believable manner. Prakashraj's hatred for Sarath has a strong basis and is also well brought out through his acts like having his sons 'practise' murdering the old man in his own backyard. Owing to Sarath's bitter experience in the past, his romance with Nayanthara also proceeds in a different manner and is dignified and mature.

The movie, which is on strong ground when focussing on the friendship between Sarath and Napoleon, stumbles when it is dealing with the rupture of this friendship. Sarath's act of making Napoleon wait outside the door when he comes to fix up Nayantara's marriage is extremely cinematic and artificial inspite of his explanation. The actual break is also too fast considering their long history of friendship. It is unbelievable that Napoleon suddenly believes the new police officer over his friend of so many years. I am in two minds about the sequence of events in the climax. On one hand, the film avoids the bloodbath that typically closes any movie that focuses on caste tensions. On the other hand, it seems like a rather lame and easy finish considering the buildup leading upto it.

As always, Sarathkumar shines in the older man's role. Makeup and body language help in bringing before our eyes a soft, peace-loving old man wisened by the years. He is usual self in the younger role, fighting with gusto and carrying out his father's wishes. Nayanthara is a welcome find. She is pretty in a homely way and doesn't ham up the few emoting chances she gets. She could have avoided the navel-bearing dresses that show off her figure quite unflatteringly in the song sequence. Napoleon is dignified while Prakashraj is believable as the caste-obsessed man carrying a vengeance. Vadivelu as a cinema theater owner raises laughs in a couple of his sequences. The one where the moviegoers don't enter the theater after seeing the name of the movie and the one where he cleverly makes up for losing the last reel of Arunachalam raise good laughs.