Hum Dono is a story about Vikram Saigal, who has two sons - Vishal and Raju. Vishal stays with his father and takes care of the family business, while Raju is his illegitimate child who works in a garage and has no relationship with his father. Raju is in love with Priyanka, but Vikram opposes their relationship as Raju is poor and wants Priyanka to marry Sameer Choudhary.
Shreechand, Vikram's brother-in-law, along with his partner Arjun Choudhary, kills Vikram for his property. After Vikram's death, it is revealed that he had divided his property between his two sons in his will. To pay off creditors and claim his share of the property, Vishal must bring Raju to live with him.
Raju, who has always been resentful towards his father, refuses to have anything to do with him. This forces Vishal to bring Raju forcefully to their house. During their journey, they face murder attempts from Shreechand, making their survival even more challenging.