Best friends Vani "Vasu" Subramaniyam and Radhika are carefree pranksters at a prestigious ladies' college in Chennai. They stay up late, break rules and wreak havoc at their hostel, much to their lecturers' annoyance. They also form a rivalry against Gita, the college queen bee. Malathi, Radhika's aunt, wants her niece to complete her studies, so that she can take over her late parents' multi-million business. In order to straighten Radhika out, Malathi arranges for her to get married.

At this point, Vasu and Radhika are introduced to Gayathri, a fiercely independent and strong police officer and an alumnus of their college. During an event at the college, Gayathri explains how women in the country lose their independence and livelihood after getting married. Convinced that they should avoid marriage as long as possible, Vani and Radhika pretend that Radhika has a boyfriend from overseas, named Ramesh, in order to avoid Malathi from arranging anymore suitors. However, this fantasy takes a whole new turn when an actual person named Ramesh calls and sends Radhika letters, claiming to be her boyfriend. To end this nuisance, Vasu and Radhika invite Ramesh to their hostel during the college dance program and plan to trick him into blurt out the truth. Vasu instructs Radhika to bring her aunt's guns for their safety.

However, a mysterious shooter kills Ramesh before the girls can confront him. Fearing that suspicion would fall on them, they decide to dispose of the body by hiding it in the air ventilator. Unexpectedly, the body slides down the vent and lands on the auditorium stage, in the middle of a performance. Gayathri, who is the guest of honour at the event, takes charge of the case. She finds Radhika's necklace on the body and the two girls are brought in for questioning. At the police station, an old woman shows up claiming that Ramesh is her son and has gone missing. Realising that the noose is tightening and that the story of their innocence would not stand, Vasu and Radhika escape police custody and hide in an abandoned mansion on the outskirts of the city.

Now the prime suspects of Ramesh's murder, they decide to find the real killer before Gayathri catches up to them. Vasu suspects Malathi of framing them in order to inherit Radhika's wealth. When they finally meet her, Malathi explains that she had known all along that the girls had been fooling her. The young man who was pretending to be Ramesh, was actually a family friend, named Vikram, whom Malathi had been planning to marry Radhika off to.

Through their college friends, the girls discover that Gita had gone missing on that fateful night. After much difficulty, the girls find Gita hiding in at a border town. However, Gita reveals that she too is on the run from Gayathri, because she had witnessed Gayathri killing Vikram that night. On the night of the murder, she had returned to the hostel to take some medications and had inadvertently witnessed the murder and had fled from the scene, fearing Gayathri would use her influence to cover up the crime. Unfortunately, Gayathri manages to catch up on the trio. However, the woman who had pretended to be Ramesh's mother arrives on the scene. She turns out to be a CBI officer, who had been investigating Gayathri and knows that the girls are not responsible for Vikram's murder.

Gayathri ends up having a mental breakdown. The CBI officer reveals that Gayathri had murdered Vikram to avenge her sister's paralysis. Vikram had raped Gayathri's sister in the past after Gayathri found out he was a womaniser and stopped her sister from dating him. To escape justice, she had no choice but to frame Vasu and Radhika as the murderers. The film concludes with Gayathri institutionalised at a mental asylum where the three girls, now close friends, pay her a visit.