The film focuses on two love stories in Chennai and Tiruchirappalli; one takes place in the period of a day, while the other ensues for months.

The film starts with an accident. Then it flashes back several months before when Amudha, a native village girl from Trichy, arrives in Chennai for a job interview, but her sister is unable to meet her to direct her to her destination. Amudha enlists the aid of a stranger named Gautham, who agrees to take her as far as the bus stop. However, he ends up travelling with her the entire day, waiting for her during her interview, and dropping her off at her sister's home in the evening. In the course of the day, she comes to understand him and becomes fond of him. While remaining calm and reserved, Gautham reciprocates her feelings. The following day, Amudha returns to Tiruchi, where she realizes that she has fallen in love with Gautham and rejects marriage proposals that come her way. She decides to return to Chennai to meet him. Meanwhile, Gautham realizes that he has fallen in love with Amudha and decides to go to Tiruchi to find her, despite not knowing her address and other any details except her name.

A parallel story follows. Kathiresan, a metal shop worker, harbors feelings towards his neighbor Manimegalai, a nurse. Being shy and soft-spoken, he does not talk to her but continues to watch her every morning for six months. Manimegalai is bold and forthcoming; she agrees to his love and orders him around mercilessly. She puts him through several tests: having him meet her father (a policeman), her former one-side lover on his own, makes him undergo an HIV test, and gets him to agree to organ donation. She wants him to decide on the basis of all that she has put him through as to whether he wants to marry her and spend the rest of his life with her; Kathiresan responds affirmatively. The two grow to love each other unconditionally with their families' consent.

Kathiresan decides to take Manimegalai to visit his family in Arasur, a village near Villupuram, and the two board a bus to take them there. Meanwhile, Gautham boards a bus to return from Tiruchi – the same one that Kathiresan and Manimegalai are travelling in. Simultaneously, Amudha boards a bus to return from Chennai. A few glimpses of other passengers are also seen: a mother and her child, a girls' athletic team, a newly married couple, two college students who are attracted to each other, and a man returning from Dubai to see his five-year-old daughter for the first time.

At a distance from Viluppuram on the Chennai-Tiruchi National Highway (GST road), The SETC bus is redirected into the opposite lane, as one of the lanes is under construction. However, before a contract carriage (omni) bus named sky travels is redirected, a tarp from a truck blows off and blocks the windshield. Unable to see where he is going, the terrified driver accidentally swerves into the path of the SETC bus. Both the buses collide head-on, killing about 35 people on the spot. Many others die en route to or at the hospital. Gautham sees a severely injured Amudha on the other bus, and she is rushed to a hospital .she reaches the hospital along with Gautham, Kathiresan has succumbed to head trauma. At the hospital, Gautham confesses his love to Amudha at her bedside, and she manages to regain consciousness. Kathiresan's body is taken away by a hysteric Manimegalai and his grieving parents.

The site of the crash is declared an accident prone-area, and the film ends with a message on road safety.