Usually in the love triangle geometry it is either a "one girl - two guys" formula or a "one guy - two girls" formula. Unnai Ninaithu is based on the latter one with Surya, Sneha and Laila forming the triangle. Like in any other Vikraman's story where the hero is not any multi-millionaire jobless youth chasing girls but a striving to be successful, humble receptionist of a lodge. A new manager moves in with his family to take over the responsibility of the lodge. Sneha is his daughter. She starts developing a soft corner for Surya. Sneha discovers that Surya was earlier in love with Laila. Though his salary is not as big and generous as his heart, Surya affords to educate an intelligent yet relatively poor Laila. But while he is away on some trip a friend of Surya befriends Laila's father, taken by Laila's beauty. Thalaivasal Vijay (Laila's father) convinces himself that it would be a worldly wise desicion to get Laila married to the wealthier friend than Surya. When Surya returns he is morose from Laila's betrayal. But later on he finds that his wealthy friend cheated Laila, so he puts all the betrayal and hurt behind to still educate Laila into becoming a doctor. While the director manages to teleport us back to future, we find Sneha still in love with Surya. The movie ends in a typical railway station scenario where the hero makes his choice between the two lady loves. The songs of Sirpi also have a Vikraman stamp to them.