The boy grows up to be Dhanush, who runs a food stall and conceals his toughness under a meek exterior (but he still has a reputation for being a badass). His brothers Muthuvel and Manickavel (Sundeep Kishan and Kalidas Jayaram) are more reckless and frequently get into scrapes. The sister Durga (Dushara Vijayan) is the apple of Raayan's eye, and he is closer to her than the brothers. They have a father-figure in Sekhar (Selvaraghavan) who'd helped Raayan out after he escaped from his village as a child with his siblings.
The main plot is driven by a devious police commissioner (Prakash Raj, stereotyped but effective) that engineers a quarrel between local dons Durai and Sethu (Saravanan and SJ Suryah) with the idea of eliminating them both. One of Dhanush's brothers gets somehow implicated in this quarrel. To protect the family, especially the sister scheduled to be married, Dhanush has to kill one of the dons. This sets into motion a second set of events, one that tears the family apart, and ignites a trail of bloody vengeance.
Raayan's script is a mixed bag: on one hand it's filled with the usual cliches and eye-rolling contrivances of a star-driven film, but on the other, it explores nuances not normally seen in mainstream masala. The dynamics between the brothers, and the transformation of the hitherto pampered sister into an avenging angel justifying her name infuses freshness into the stereotypes - Dushara Vijayan in the film's second half is a revelation - the scene where Durga fends off an attack by goons on a mortally wounded Raayan is nail-biting, and she becomes the main driving force of the vendetta. One applauds Dhanush for permitting her to overshadow his own character. Even the shading of the bad guys is interesting - there's some wicked humor courtesy Suryah's Sethu getting buffeted between his two wives.
There is also some serious visual chutzpah on display, especially in the action scenes and the choreographed festive number that comes late in the film. Om Prakash's cinematography uses overhead tracking shots, slow motion and colors in spectacular ways. If Raayan's script had lesser concessions to 'mass' pandering this could have been an amazing masala movie. But it still has several moments of interest, per se.