Saravanan(Prithviraj) is an assistant director who feels he has written a script that only he, as a director, can do justice to. Mythili(Gopika), a leading heroine, is in love with Saravanan but is willing to wait until he gets his big break as a director. Kanniah(Prakashraj), who has been looking for a break as an actor for even longer than Saravanan, becomes Saravanan's roommate. When Saravanan goes to Hyderabad, Kanniah copies his script and pitches it a producer, under the condition that he has to play the hero in the film. Impressed by the script, the producer agrees to the condition. The movie turns Kanniah, now rechristened Dilipkanth, into a star and Saravanan, who now has another story, finds that he can't make his film unless Dilipkanth plays the hero.

Films set in the film industry are rare and so hold a special appeal since they give us a behind-the-scenes look at the industry. While we look at the glamor and the glitz of films everyday, such films give us a peek into what goes on in the background. Vellithirai too has this appeal. The stuggles of Prithviraj and Prakashraj show us the stark reality of how difficult it is to break into cinema. At the same time, the movie can almost be termed inspirational with some of its positive dialogs("there are no non-actors; just people who haven't gotten the chance yet") and its message that if one tries hard, one will definitely get that all-important break.

Udhayanaanu Thaaram worked as a satire on the Malayalam film industry and its stars with the script taking potshots at almost all the big stars as well as the workings of the industry itself. The inability of our Tamil cinema stars - and their fans - to take a joke has been showcased pretty clearly in the past and so director Viji understandably shies away from repeating that aspect of the original. So a major part of the film's appeal is blunted. A couple of throwaway lines(like on the longevity of our heroes and their affinity for titles) apart, the film plays it safe and leaves our heroes unscathed. Prakashraj, once he becomes a star, is pretty much a caricature and so his actions and dialogs are too over-the-top(asked what he would have become if he hadn't entered cinema, his response is to ask what would cinema have become without him!) to be realistic and considered as veiled attacks on our real stars.

There are no such complaints about the climax though. With Prithviraj suffering for almost the entire film and Prakashraj earning our dislike, the film makes us wait for Prithviraj to get his revenge. So it is delicious when he gets it and doubly so when he gets it in an intelligent, crowd-pleasing fashion. His plan is clever and it is nice that even after knowing Prithviraj's plan, we don't see all parts fall into place(with the help of some clever editing) until the very end and even if we are not as stunned as Prakashraj is, we are a little surprised too. Prithviraj's plan has been seen twice before - in the English original as well as in the Malayalam version - but it still hasn't lost its appeal and makes us cheer whole-heartedly.

Prithviraj is the perfect choice to play the good-hearted, idealistic assistant director. He is able to put aside the humorous side that we saw in all his roles so far and convey his passion and strong ambition of making it as a good director. But there are times, before the climax, when we feel he has underplayed his role a bit too much and is almost a doormat. Prakashraj bites into his character with relish. Characters who hide their villainy under a smile are always more easy to dislike and he uses that to full effect. Gopika looks surprisingly jaded, especially since she plays a top actress. I'm not sure if she acted without make-up or something like that but it hasn't worked. Lakshmirai makes a rather late appearance but gets to play an important role after that. Kumaravel is impressive as Prithviraj's friend while Baskar gets a few laughs as Prakashraj's manager.