Kundavi (Jyothika) was brought up in a small village called Ambasamudram. She, along with her two friends, decide to have a love marriage. However she is not so successful. Her father arranges her marriage to Gowtham (Suriya Sivakumar) against her wishes. Both look gloomy during the wedding due to obvious reasons.

Six years later in Mumbai they have a five-year-old daughter Ishwarya (Shriya Sharma) and live as a happily in love married couple. Gowtham works as the chief mechanical engineer at Maruti Suzuki and Kundavi works at a local call center. Gowtham goes to New York City for a short period. During this time, Kundavi comes across Gowtham's old college diary. Gowtham wanted to be an engineer from a young age and forced his father's brother to pay for a seat in Coimbatore for mechanical engineering. From the second year of college he is the don. In college, he is attracted to Ishwarya (Bhumika Chawla), whose father is a Coimbatore MP. Gowtham and Ishwarya fall in love and decide to get married. At the registrar's office after Gowtham ties the knot, Ishwarya's father and his men beat him up, separating the lovers and sending Ishwarya off to Sydney, Australia. At the end of the diary, Gowtham writes a note: "If I have one wish, it would be to live with Ishwarya happily at least for one day." Then, due to his uncle's last wish at death bed, Gowtham agrees to marry Kundavi.

Gowtham returns from New York and finds his wife changed. She works late and avoids him. Once Kundavi finds out he does love her and how much he missed her during New York trip, she finds his lost love who had just returned from Australia. Ishwarya has become a modern girl in contrast to the demure salwar kameez girl she was in college, and completely ignores her father at the airport due to his past behaviour with her. Kundavi asks Ishwarya to visit them and she tells her husband that he should live happily with Ishwarya for a day and that for that one day, she and their daughter do not exist for him, and leaves Gowtham with Ishwarya.

Gowtham spends the day with Ishwarya. They travel to many places and do many things and recollect their memories. Ishwarya and Gowtham share their love for each other and how they missed each other during these 6 years of separation. They eventually fall in love with each other all over again and soon get intimate. It is then revealed that all these things were just Kundavi's dream. Panicked by the dream, Kundavi decides to check up on them. When she gets back home dreading, she finds her husband alone. She asks him where Ishwarya is and finds Ishwarya's letter. In it, Ishwarya says that Kundavi gave them a day, but an hour was sufficient for them. 40 minutes of silence, 10 minutes of formal inquiries and 10 minutes of talking. Even in that 10 minutes talk with him, the words that came out of Gowtham was 'Kundavi' only. Ishwarya realises that they both are immensely in love and leading a very happy life. She wants to love Gowtham in her next birth also. But not as Ishu, but as Kundavi. She wishes the couple a happy life and leaves, never to return.

In the end, Gowtham confesses that he had hidden the secret of loving someone so that Kundavi doesn't get hurt as any girl would not bear her husband's love being shared. However, unlike others, Kundavi has brought the girl her husband loved in order to make him happy. They then cry in happiness and hug each other while Diwali fireworks blossom. Their daughter Ishu also joins them and the movie ends on a happy note.