Munnabhai (Sonny Dutt) is a dreaded but a good-hearted underworld don of Mumbai. The police are trying to implicate him on criminal charges but so far they have not been successful because of lack of evidence. Once when Munnabhai is beating up one of his foes, he sees Kamal (Aishwarya Rai) and he is smitten by her beauty. He starts visualising her wherever he goes. Because of this he stops taking part in his usual underworld activities. His men decide to take him to Dr. Rastogi (Amitabh Bachchan). The doctor realises that it's a 'love virus' and advises him to woo the girl, not realising that the girl is nobody else but his own sister Kamal. Munnabhai starts wooing Kamal. But she is in love with Raja (Ajay Devgan). The doctor is ignorant of their love affair. Munnabhai makes the doctor's life miserable because Kamal does not respond to his advances as per advice given by the doctor. It's not long before the doctor realises that his underworld patient has been in love with his own sister, so he decides to take her to Malaysia and get her married off, This puts Raja in a dilemma. He can't tell the doctor about his love because of his social status and he can't even let Kamal get married to someone else in Malaysia. Will the doctor be able to save Kamal from the don? Will Raja be able to convince the doctor and Munnabhai about his love? This is a rip-roaring comedy directed by the don of comedy films, David Dhawan.