Singaravelan, Kamal Haasan known as Velan, lives with his widowed mother Parvathy Sumithra in a quiet village. Their family history is tense: Velan's father died heartbroken after his marriage to Parvathy was blocked by her sister-in-law, leaving the kinship fractured. The locals believe Parvathy’s supposed curse led to the car accidents that claimed her brother and sister-in-law, and a guardian’s promise bars their daughter from marrying Parvathy’s son. Parvathy reveals Velan’s duty to marry her brother’s daughter Sumathi Khushboo to reunite the family, so with only a photograph of Sumathi as a child, Velan heads off to Madras to fulfill the mission.
Velan arrives at his friend Mano’s Mano house, where three roommates—Mani Goundamani, Subha Vadivelu, and Ramasamy Charle—await the plan. Velan explains the assignment and his companions eagerly agree to help. At a computer center, a clerk conjures up an image of Sumathi as a teenager. On a sunlit beach, Velan and the crew spot a woman playing tennis who is Sumathi. When Sumathi goes to fetch a ball from the sea, Velan dives in to help and accidentally submerges her, though he manages to pull her out. After waking, she berates him for not knowing how to swim. Despite his friends’ warnings to abandon the pursuit because of her arrogance, Velan stands his ground.
The group tails Sumathi to a five-star restaurant where a flute musician performs. After the set, Sumathi kisses Velan’s hand. Velan offers his own hand for a kiss, and she asks if he knows anything about music. To prove his skill, Velan performs a playful display—singing while wearing a variety of instruments—but Sumathi scoffs at the performance. Velan’s light teasing only deepens her disdain.
To win over Sumathi’s guardian, Thaiamma Manorama is visited daily and impressed by Velan’s lively, entertaining nature. He even fabricates a story claiming his mother’s name is Mahalakshmi to seem respectable. Thaiamma nods in approval, but Sumathi remains wary. Sumathi’s uncle Natesan Jaishankar, a retired IG, arrives to warn Velan to stop pursuing his niece. Velan realizes his father is Kaliannan Gounder, an industrialist who disowned him for pursuing music. Kaliannan confirms the family backstory, a truth Velan and his friends had already nudged him to reveal to help their cause.
Over time, Velan wins Sumathi’s heart and their bond grows stronger. A pivotal moment comes when Sumathi learns Velan was attacked by men hired by Natesan after the deception about his lineage is exposed; Velan is shown in a hospital setting, bearing bandages as part of a staged show to prove his resolve. Velan’s mother rushes to the hospital and, upon learning the truth, feels a sense of relief. Their love deepens and they decide to get engaged.
On the engagement day, through Sivamani Nizhalgal Ravi, the manager at Sumathi’s factory, Sumathi discovers Velan is Parvathy’s son and cancels the engagement. Natesan learns that Sivamani is printing counterfeit bills at Sumathi’s premises. Sivamani murders Natesan and frames Velan for the crime. Velan escapes the police while his mother, Kaliannan, and friends are arrested as accomplices.
Sivamani escalates his plot, intending to kill Velan and marry Sumathi for her wealth, and uses Thaiamma to push the proposal. A plan is set to capture Velan, but the hero fights off the henchmen and, with the help of the police, reaches the wedding hall to confront Sivamani. The villain is exposed and arrested, and Sumathi recognizes Velan’s genuine love. She pleads with her mother to bless the union, and Velan and Sumathi marry in a heartfelt, long-awaited celebration.
