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 Gautham (Surya Sivakumar) against her wishes. Both look gloomy during the wedding due to obvious reasons.
Six years later in Mumbai they have a 5-year-old daughter Ishwarya “Ishu” Gautham (Shriya Sharma) and live as a happily married couple. Gautham works as the chief mechanic at an automobile company and goes to New York City for a short period. During this time, Kundavi comes across Gautham’s old college diary. Gautham wanted to be an engineer from a young age and forced his father’s brother to pay for a seat in Coimbatore for automobile 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. Gautham and Ishwarya fall in love and decide to get married. At the registrar’s office after Gautham ties the knot, Ishwarya’s father and his men beat him up, separating the lovers and sending Ishwarya off to Australia. At the end of the diary, Gautham writes a note: “If I have one wish, it would be to live with Ishwarya happily at least for one day.”
Gautham returns from New York and finds his wife changed. She works late and avoids him. She finds Gautham’s lost love Ishwarya, who had just returned from Australia. Ishwarya has become a modern girl in contrast to the demure salwar kameez girl she was in college. 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 Gautham with Ishwarya.
That day Gautham spends with Ishwarya, Kundavi imagines them to have a good time and eventually fall in love with each other all over again. When she gets back home, dreading, she finds her husband alone at home. She asks about his day with Ishwarya, and he gives her a letter written to Kundavi from Ishwarya. In it, Ishwarya says that within five minutes of speaking to him, Gautham mentioned ‘Kundavi’ so many times that she realised that he loved his wife very much and is leading a very happy life. She wishes the couple a happy life and leaves, never to return.
In the end, Gautham confesses that he has hidden the secret of loving someone so that Kundavi doesn’t get hurt as any girl wouldn’t 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 Ishwarya also joins them at the end and the film ends with a happy family celebrating Diwali.