Jambhavan movie is about Velan (Prashanth) who is a responsible son of a village landlord (Vijayakumar). Adored by the villagers for his good deeds, Prashanth gets a shock when Vijayakumar informs that he is his foster son.
A shocked Velan sets out on a mission to know about his past. He reaches Chennai and comes to know that his family members were killed by a dreaded gangster Deva (Vijayan). He had then vowed to kill him and his gang. In the name of Jambhavan, he starts to kill rowdies in the society.
Suffering an injury in his head, Velan loses memory and is later adopted by Vijayakumar. He comes to know that his job was just half-done. The rest is how he puts an end to Fefsi Vijayan and his men coming to Chennai.