Karthik Varadarajan is an independent and free-spirited software engineering graduate from a wealthy family who co-owns a startup along with his friends. At a friend's wedding, he meets Shakthi Selvaraj, a medical student from a middle-class family. The duo constantly bumps into each other on the local commuter trains they both ride, and they soon fall in love. Karthik aggressively pursues Shakthi and asks his parents to formally ask her parents for her hand in marriage. Shakthi, however, is reluctant. Karthik manages to convince Shakthi and requests his parents to formally ask Shakthi's parents for her hand in marriage. When the parents meet, they do not get along, and Shakthi calls off the relationship altogether and leaves for an extended medical camp in Kerala.
While apart, both Karthik and Shakthi realize that they are desperately in love and decide to get married without the knowledge or consent of their parents. They continue living separate lives after marriage, meeting outside of their homes and hoping that their parents will see eye to eye at some point in the future, and can be informed of the marriage. However, when the family of Hyundai executive Raghuraman arrives at Shakthi's house one day to discuss a prospective wedding alliance between Raghuraman and Shakthi's elder sister, Poorni Selvaraj enters the picture, and the situation becomes more complicated. Shakthi's parents attempt to fix her marriage to Raghuraman's younger brother Shyam. Shakthi confesses to her parents and Raghuraman's family that she is already married, leading to the alliance being called off and her parents throwing her out. Karthik also divulges the same to his parents and is asked by his father to leave his house.
Karthik and Shakthi start living together in a partially constructed apartment, and while all goes well for a while, they soon find that marriage is not as easy as they expected, and living under the same roof results in a large number of conflicts. Shakthi soon learns that her father has been diagnosed with jaundice and requests Karthik to visit him at the hospital. Karthik declines, citing her father's hatred of him as the main reason. He eventually agrees to meet him the following day, but by the time they reach her house, Shakthi's father has died. Wracked with guilt, the two return home, their relationship taking a turn for the worse. The two stop talking to each other.
Meanwhile, Karthik takes it upon himself to fix Poorni's broken alliance with Raghuraman. He arranges a blind date between the two, which initially fails. However, with more meetings, Poorni and Raghuraman become closer. This development takes place without Shakthi's knowledge. Shakthi eventually learns from Poorni about her husband's efforts to get her married and is overcome with guilt. Karthik sets off on the same evening to the railway station to pick up his wife as is their usual routine. In her rush to get home and make up with Karthik, Shakthi meets with an accident. Karthik waits for her, and as she fails to turn up, he searches desperately for her throughout the city, ultimately discovering her in the ICU of a hospital. Shakthi is registered under another name and is in a coma after having undergone brain surgery.
An IAS officer, Ram, claims that he caused the accident and admitted Shakthi to the hospital. As Karthik vents out his frustration on Ram, Ram's wife intervenes and lets Karthik know that she was the person who caused the accident and injured Shakthi, and her husband was merely trying to protect her by taking the blame himself. Karthik observes Ram and notes that he has a lot to learn from the latter. He proceeds to see Shakthi and admits that he could have been a better husband. Shakthi wakes up from her coma, and the two reconcile.
