HUM Kisise Kum Nahin sees Sanjay Dutt playing an underworld don who suddenly becomes besotted with the beauty of (Komal) Aishwarya Rai. He enlists the help of a 'brain doc', Big B, who unwittingly advises him to tell his new found desire how he really feels.

He does this not knowing the lady in question is none other than his own sister. Meanwhile Komal is in love with local 'loser' Raja (Ajay Devgan).

Once Big B realises what's going on he sends his daughter to America to try and get her married to some respectable bloke. And so begins a series of comical misdemeanours which sees the Doc and Ajay go head to head and then Mr Dutt prove he's so much better when he plays a bad guy.