The movie revolves around Munnabhai (Sanjay Dutt) a dreaded but good-hearted underworld don of Mumbai. Once while beating up one of his foes, he sees Komal (Aishwarya Rai) and is so smitten by her beauty that he starts visualizing her wherever he goes and in whatever he does. Not understanding this new phenomenon in Munnabhai''s life, his men take him to Doctor Rastogi (Amitabh Bachchan) . The Doctor realizes it''s a love virus so he advises him to woo the girl somehow, not realizing that Munnabhai has fallen for none other than his own younger sister Komal. Munnabhai starts wooing Komal but she is in love with Raja (Ajay Devgan), a local vagabond doing nothing except working in a bowling alley as a bouncer. It is not long before the doctor realizes that his underworld patient is in love with his own sister, so he decides to take her to Malaysia and get her married off. Raja also manages to go to Malaysia with them. Not one to be left behind, Munnabhai also follows them and all beans are spilled when the doctor comes to know about Raja and Komal's affair and Munnabhai's intentions. Helpless and powerless in Malaysia, Munnabhai plays a smart one on them and all are deported back to Mumbai where the don is the uncrowned king. What happens after they land in Mumbai? Will the doctor be able to save Komal from the Don? Will Raja be able to convince the doctor and Munnabhai about his love?