Narayanan (played by Madhavan) is a young, handsome astrologer from the small, orthodox city of Vaarana in Tamil Nadu, who is well known in the town for his accurate predictions and trustworthiness. Because people of the town know his ability to keep their secrets to himself, they don't hesitate to reveal their familial affairs to him. As a result, Narayanan knows the secrets and ongoings of almost every family in the town.
Narayanan secretly loves Radha, the only daughter of the city's school teacher Pattabhiraman. Radha however, is probably the only one who doesn't visit Narayanan to seek his astrological advices as she doesn't believe in them. In fact, she hates Narayan for she thinks he is misleading people with his unscientific predictions, although she doesn't show it outside.
When Radha's marriage gets fixed with Kumar, a doctor from the neighboring city, Pattabhiraman brings their horoscopes to Narayanan for his predictions. Narayanan finds the horoscopes totally incompatible, to an extent that an alliance between those two horoscopes would result in severe consequences to the family members of both sides - technically 'griha-dourbhagya dosham'. Upon hearing this, Pattabhiraman decides to cancel the wedding. That doesn't go well with Radha who believes horoscopes and predictions are baseless. She visits Narayanan and takes him to task severely. She lambastes him saying he virtually destroyed her life and tells him that there's nothing she hates more than him. Despite that, Narayan continues to maintain a soft corner for Radha.
She then goes to her father Pattabhiraman and says she wants to and will marry the same person Kumar no matter what, or she would remain unmarried for life. With no other option, Pattabhiraman agrees to get her married to Kumar and they get engaged. Entire town but Narayanan would get the invitation for the wedding.
Two weeks before the marriage, while Kumar and Radha are engaged, both their families visit a temple in their ancestral village. After the temple visit and pooja, family decides to offer prayers at the holy river. While playing in the river casually with the family after the prayer, including with her nieces and cousins, Radha accidentally pushes a few of them into the river. Due to its vigorous flow, three of them, Pattabhiraman, Kumar's mother and a first cousin of Radga get carried away in the current. All three of them die in the mishap.
This leaves Radha terribly confused and she starts questioning her beliefs. Her stand on Narayanan's predictions and impression on Narayanan himself softens very much.
Kumar gets angry, cancels the wedding and blames Radha for deciding to go ahead with the wedding just to prove Narayanan wrong. This dejection and blame from Kumar, together with the mockery from others from the neighborhood leaves Radha shattered and she leaves the town. She goes to Shimla for her post graduation studies at a reputed institute.
While in Shimla, she falls in love with her handsome fellow student, Amogh. Amogh, a Delhite, also doesn't believe in horoscopes but now, Radha does. She returns to Vaarana to talk to her mother about this alliance with Amogh. This time though, she visits Narayanan, apologizes for her previous behavior and gets friendlier. Narayanan mistakes this friendliness for love and starts fantasizing about her, unaware of the fact that she is in town for her marriage talks.
The next day, Radha and her mother visit Narayanan to seek his advice and predictions regarding her marriage to Amogh. Narayanan is devastated. He sincerely hopes that the horoscopes don't match, but they perfectly do. But his love for Radha blinds his ethics and he lies to them that this marriage will only result in more agony and disasters for both the bridegroom's and bride's families.
Having learnt a lesson once, Radha and her mother decide to cancel the wedding and she stops seeing Amogh altogether. She curses her own fate for being so harsh on her.
As days pass by, Narayanan and Radha get closer and Narayanan finally proposes to her one fine evening, bursting out his feelings that were kept hidden for years. Radha, although not really in love with him, accepts his proposal, owing to her mother's and relatives' pestering to get married soon.
Narayanan and Radha get married and things go really well for a couple of months. Narayanan showers all the love on her and she is equally happy and glad.
Out of curiosity, she slowly starts learning to read horoscopes and Narayanan, unaware of the consequences, gets over enthusiastic in teaching her. As she picks up predicting and analyzing horoscopes, disaster awaits. One morning, she gets really curious and tries to match her and Amogh's horoscopes. The result leaves her tattered. She's broken and loses all her trust, not just on Narayanan but on the entire world, on her life and purpose, on her feelings.
As Narayanan returns home, she takes him to the KaaLi river shore. By the very uber-serious look of her face, Narayanan sort of realizes that something is wrong. He's all sweating as she holds out to him her horoscope and asks him to predict what's in store next for her. He's trembling, voice not coming out. With shaking hands, he lets her horoscope fly out as she slowly walks backwards into the overflowing river.