Ullasam is a story about two fathers, Raghuvaran and S.P. Balasubramaniam, and their two sons, Vikram and Ajith. Raghuvaran is a criminal smuggler who has an influence on S.P. Balasubramaniam's son, Ajith. Ajith is determined to become a criminal mastermind like Raghuvaran. Ajith's father will do anything to deter his son from following in the footsteps of Raghuvaran, but his efforts prove futile. In a state of frustration and anger, Ajith's father decides to take a different course of action. He decides to raise Raghuvaran's son, Vikram and teach him about values, virtue and hard work. This unconventional decision has a significant effect on the two sons who eventually go off to college and fall in love with the same woman.