Vallavan (Silambarasan) is a happy-go-lucky college student with a set of friends, Bala (Santhanam (actor)), Subbu (Sathyan Sivakumar), and Suchitra (Sandhya (actress)). When they are at the temple, Vallavan sees Swapna (Nayantara). He immediately falls in love with her. While Vallavan is at the college, Swapna shows up. She is revealed to be a teacher who is three years older than Vallavan. He decides to woo her by turning into Pallan, an ugly duckling with buck teeth and glasses. Pallan makes Swapna fall in love with him for his heart, even though he is ugly.When Swapna comes to know that Pallan is younger than her (from one of Vallavan's enemies in school) and also a student, she dumps him and decides to marry another man. Meanwhile, a sequence of events take place, much to the chagrin of Vallavan, who is highly insulted by them. As Vallavan walks in the streets wondering how things got so messy, he recalls his school life. When he was in higher secondary school, Vallavan met Geetha (Reema Sen). A hysteria Geetha ensures that Vallavan is mad about her. Coming to know of her true nature, he ends the affair with her, but she is not ready to let him go so easily, so he resolves to teach her a lesson. Geetha returns for payback. She tells him that she was the spoilt sport for the current mess in his life. In a climax displaying her disorder, she kidnaps Suchitra, and Vallavan arrives and frees her. The film fast-forwards to three years later. Geetha is released from a mental asylum. The moment she steps out, she exhibits her fiery psychotic expression, showing that she never actually recovered. Vallavan is waiting for her, and they communicate telepathy, with Vallavan saying that she cannot do anything to him.