Karthikeyan (Arjun) is a photographer-editor working in Indian Express in Bombay. Chitra (Meena) is a bank employee. Both reside in Navi Mumbai. Karthik meets Chitra while opening a bank account. While returning home, he again meets her in a train. He offers his seat, but she does not want to accept it. During a train strike, he invites her to travel in an auto to reduce expenses, but she declines. When Chitra hesitated to travel in the same train with Karthik, he becomes exasperated and explains that he only talked to her because both are from the same locality, both are Tamilians, and he promises her that he will never talk to her again. After some days Chitra voluntarily talks to him. Karthik, in return, accompanies her to a police station to get back her snatched handbag. Karthik invites Chitra to his home to meet his parents.

Karthik's parents like Chitra and all become friends. Weeks later, Karthik's mother requests Chitra to tell Karthik to get married. When she conveys his parents' wish, Karthik explains about his late wife Aruna (Jyothika). Eight years earlier Karthik was a police officer with the bomb defusing squad. Though Aruna did not want Karthik to endanger his life every now and then, she does not tell him to quit, due to her respect of his desire to work as defuser. While Karthik and Aruna are in Tirupur to attend Aruna's friend's marriage, Karthik is pulled to Coimbatore to defuse a bomb, and he accomplishes. But Karthik's colleague and friend Ajay loses a leg in another defusion work. Karthik goes to Chennai to meet Ajay, who tells him about Aruna's fears. Karthik quits from Bomb squad and informs Aruna. Aruna, in a bid to soon meet Karthik, leaves to Chennai by train. Due to a signalling error, her train collides head on with another train and she passes away. Karthik then quit the police job and moved to Mumbai .

Chitra then tells Karthik about her life. She was a graduate in Chennai living with her brother's family and searching for a job. She meets SBI officer Srikanth (Ramesh Aravind) through various accidental events, and they fall in love. While Chitra's family do not object to the marriage, Srikanth's Brahmin parents in Ooty object to the marriage. Srikanth disobeys them and marries Chitra. Within hours of the marriage, Srikanth receives news that his mom is on death bed. When he goes to Ooty, he finds that his dad lied to him, and his mother banishes him forever. Distraught, he leaves to Chennai by train, and died in the same train accident as Aruna. As per her husband's earlier wish, Chitra adopts a baby boy, Shiva. Her brother got a good job offer in Singapore and Chitra forced them to leave her. She got Srikanth's job from the bank due to his untimely demise and thus she had moved ahead. Knowing all this, Karthik's parents want them to get married.

Shiva moves close to Karthik and his family, while Chitra tries to prevent relations with Karthik. Karthik's father (Nagesh) understands Karthik's interest towards Chitra. He asks her to marry Karthik. She refuses, and once for all, avoids Karthik. Karthik understood her intention and stayed away from her. Chitra meanwhile gets confused regarding second marriage due to the trouble given by her neighbour's husband and Shiva's passion for Karthik. Chitra's neighbour once attempts to rape her; she manages to escape. Karthik, who heard about it, attacks the man for misbehaving, and makes him vacate Mumbai.

After much thought, Chitra decides to marry Karthik for herself and her son. She plans to meet him at the station to express her decision. While returning home, she meets her mother-in-law (Lakshmi) waiting for her. Chitra's mother-in-law requests her to come and live with her as she is very alone after her husband's death. Chitra applies for transfer and leaves to Ooty with her mother-in-law. She has not dared to meet Karthik and she leaves without informing him. Karthik and his family are very much disappointed by this.

After some months, Chitra panics on seeing a news about a bomb blast at Mumbai Indian Express and verifies Karthik's safety. Karthik leaves for Coonoor on an official assignment. There he meets Chitra with her mother-in-law in a shopping center. Chitra introduces him to her and tells about Aruna's death in the same train accident where Srikanth died. On hearing this, Chitra's mother-in-law invites Karthik to have lunch with them the next day. This delights Shiva. He eagerly waits for Karthik and leaves school well before, but is stuck in a traffic jam for a long time. Meanwhile, Chitra explains about her decision to marry him, and later changed it as her mother-in-law requested her to live with him.

Karthik leaves without meeting Shiva to catch the train. This disappoints Shiva. When Chitra tried to console him, he blames her because she did not keep the promise that he, Chitra, Karthik, and his parents to live together. Chitra's mother-in-law hears this, understood the meaning of it and she realised the mistake she made. She catches Karthik at the station and requests him to marry Chitra. Karthik and Chitra leave for Mumbai and get married, which delights Shiva and Karthik's parents.