The film premieres sometime in the '90s and shows a group of adolescent boys from a Catholic school all set to begin their 11th year. The bunch of friends (Vinoth, Surender/Su, Chinese, Naushad, Richard, Durai, Francis and a few others), all studying in Commerce stream, check the list of new admissions for any new girls on the day of collecting their school books. They are met by two girls (Rekha and Anu) from the same school and upon leaving Rekha looks over and waves at Vinoth. It is shown that Vinoth and Rekha have been in a relationship for the past three years and only a few of their friends know about it. One of their common interest and favourite dating activity is listening to A. R. Rahman songs in a walkman. Vinoth aspires to become a music director and Rekha is supportive of his goal, so much so, that she even gifts him a guitar for his birthday

On that same day, a girl named Victoria/Vicky joins the Commerce stream as a new admission and takes an instant liking to Vinoth. Whilst all of Vinoth's friends suspect her of being interested in Vinoth, he rejects the idea of it. While Rekha's best friend Anu is in the Commerce stream with the boys, Rekha is in the Science stream, away from the boys. Rekha often shares her feeling of having less time to spend with Vinoth now that they are in different classes. After school reopens, more students are introduced - notably, Catherine, Richard, and Francis among others; Catherine is egoistic and detests and mocks Chinese who is interested in her. Richard, though part of the friendship group, is domineering and problematically precocious. Lastly, Francis is often bullied by Richard due to his lack of 'manliness'.

Initially jealous and possessive, Rekha grows suspicious about the friendship between Vicky and Vinoth, despite Vinoth's denial and fidelity. After an incident where Rekha becomes upset at seeing Vinoth and Vicky playing basketball together, Vinoth begins to maintain distance with Vicky. On their farewell day at the end of their 12th year, Rekha learns about the relationship between Anu and Chinese and excitedly rushes to tell this news to Vinoth. At this time, Vicky requests the help of Vinoth to remove a box from a tall shelf in a secluded room. As he was lifting, a speck of dust seems to fall into the eyes of Vicky and when he tries to blow it out, Vicky kisses him on the cheek. However, Rekha witnesses the kiss and immediately rushes away from there. Both Vinoth and Rekha decide to end their relationship after an intense argument where Vinoth was unable to convince Rekha. As Vinoth goes to sleep that day, Cupid arrives and advises Vinoth to beg mercy from Rekha and patch up. Vinoth adamantly refuses and claims that he is better off without Rekha in his life and that he will not regret his decision. At the same time, a silently crying Catherine leaves earlier from the farewell event, after being almost sexually abused by a food vendor at the event. Similarly, Francis and Richard are chastised by the teachers after the teachers catch the boys drinking, although Francis was bullied by Richard into drinking.

The scene cuts to Vinoth's future in the present day, where he is shown to be a successful and famous music director, yet unmarried and void of bliss in life. At this time Chinese arrives at his house and they leave for their school reunion. Chinese is a contractor and married, but unhappy with his marriage, which he doesn't show to others. They meet up with Richard, who is happily married with two kids, yet he suffers from alcoholism.Durai, Another friend of theirs is burdened with loans as he had to marry his three sisters with hefty dowries on his own. Surendar arrives at the reunion on a sports motorbike, flaunting his bachelor's life and its freedom. Naushad, a physician, arrives with his newly married conservative wife. Anu arrives with her husband, who is overly talkative, naive, and a credulous man. Catherine gives out backhanded compliments which are hiddenly insulting. Rekha arrives with her fiancé Sid, who is uninterested in the reunion and finds it lacking class and taste to his liking, and decides to leave midway. Another friend, Joseph, who used to be Vinoth's competition in music arrives and greets Vinoth and asks for keyboard player opportunities in his upcoming projects as he is struggling. Finally, Francis, now confident and comfortable in his own skin, arrives with his partner, and seeing his partner, an overly drunk Richard shouts for him to leave. Richard's wife Sharon drives sense into Richard who later apologises to Francis for his behaviour and admits that it has been hard for him to see Francis in this light after growing up together with him having a different image of Francis in his mind.

Chinese sees how Catherine has been rudely behaving and decides to teach her a lesson by surreptitiously following her to her home with the aid of Surendar. He spraypaints her parked car, however, Catherine comes out of her home and discovers both of them hiding behind a wall. A child follows her out and calls her mum and this shocks both Chinese and Surendar. Catherine admits that she is no longer the same girl that they knew in school and that her behaviour at the reunion was done knowingly because she wanted to recreate her past self for a few hours of satisfaction and even the car parked outside is a rental car for a day. She tells them how she is now a single mother and an unmarried woman after her affair with a married professor. Hearing her story, Chinese reveals that he is waiting for his divorce finalisation after his wife cheated on him with someone else in their office. Surendar too admits that he is still trying to make ends meet as a mechanic and the bike he rode was borrowed for a day from a workshop near his. In the end, they all end up spending the night at Catherine's, cooking, eating, and laughing.

On the other hand in the reunion, Vinoth is asked to perform a song and he reluctantly grabs a guitar and sings a song which he states as the first song he had written. Throughout the song, he exchanges gaze with Rekha who is emotional at knowing that this song is written for her. She asks him if she could listen to any songs from his upcoming movies. Vinoth agrees and they both walk out of the reunion together as Vinoth had his earphones in his car. They share an earpiece of the earphones listening to the songs. Rekha asks Vinoth to play A.R.Rahman's songs which they listened to during their school time. Sid calls Rekha and informed her that he had come to pick her up. As Rekha was about to leave, Vinoth admits that he has missed her.An emotional Rekha takes Vinoth by surprise by planting a passionate kiss on his lips and leaves without looking back. The kiss crumbles Vinoth to the ground and he regrets his past decision to end his relationship with Rekha.Chinese finds him and consoles him while Cupid arrives at this scene with the past Vinoth from the 90s in the background, seemingly showing him the eventuation of his decision. Seeing this, Vinoth begs for another chance and Cupid grants him that chance to return back to the 90s. Waking back up in his room after the argument with Rekha on their farewell day, Vinoth runs to Rekha's house and apologises to her and they both reconcile.

The scene cuts to the future in the present day, where Vinoth is happily married to Rekha, who is an architect and has a child. Although he isn't a music director anymore and works a normal office job, he is happy just to have Rekha in his life. Chinese is married to Anu and directs sitcoms. Richard is married too, but this time his wife is an alcoholic, whom he has to take care of. Catherine is a successful children's author. Naushad is married to a different woman and is happy. Francis is a famous YouTuber. Surendar works in a call center and is engaged to a Nepalese lady. Joseph is now a successful music director. All of the friends are successful and happy with where their lives are. In this version of their lives, the friends are on good terms with Vicky too, who joins their reunion virtually as she now lives abroad. The movie ends with an appearance of Cupid - who Vinoth doesn't remember, though he realises to have met him somewhere - and Cupid saying how he has met up with each of the characters somewhere in their lives to direct them to make the right decisions in their love life, but none remembers him.