Nanda was Surya's breakout movie, the one that transformed him from a generic romantic hero to an actor of substance. A number of movies that came afterwards cemented that position - Kaakka Kaakka (the best cop drama in Tamil cinema bar none, in my opinion), Perazhagan (his most astounding performance to date), Pithamagan (stole nearly every scene he was in)... but Nanda was where it began.
The movie is about a boy who kills his abusive father as a kid when the guy is beating up his mom. The mom goes crazy, and believes that her son is a cold-blooded killer. The son goes to juvenile prison, and when he emerges, circumstances lead him to work as a henchman for the local bigwig (a towering performance by Raj Kiran). He's pretty good at what he does, and quickly moves up the ranks to become the Raj Kiran's right hand man. All the while, he attempts to reconcile with his mom, but all she seems to see of his is his violent side. Meanwhile, his ascent triggers the jealousy and insecurity of Raj Kiran's son. The consequences are obvious - son kills father, Nanda kills son. So far so good. But Bala has a slingshot ending up his sleeve - when Nanda comes home to eat before fleeing the town with his sweetheart (played by a surprisingly tolerable Laila), his mom poisons him, believing that her son is too much of a violent force to be let loose. Throughout the movie, we can see that she is a bit mad, but this is essentially where it all comes to a head. True, we've seen mothers kill wayward sons before (Mother India, Vaastav), but not like this. Not like this.
With a trio of offbeat movies of phenomenal power (Sethu, Nanda and Pithamagan), Bala has emerged as the K.Balachander of our time - if KB took Rajni and Kamal and made stars out of them, Bala has done that with Vikram and Surya. The difference, though, is that KB's product was relatively more mainstream. And he never hit this hard.