Munnabhai (Sanjay Dutt) is a dreaded but good-natured 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 Komal (Aishwarya Rai) and he is smitten by her beauty. He starts visualizing 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 realizes that it is a love virus and advises him to woo the girl, not realizing that the girl is his own sister, Komal. Munnabhai starts wooing Komal. But she is in love with raja (Ajay Devgan). The doctor is ignorant of their love affair. Munnabhai makes the doctors life miserable because Komal does not respond to his advances as per advice given by the doctor.
Will the doctor be able to save Komal from the don? Will Raja be able to convince the doctor and Munnabhai about his love?