Lambu is a petty criminal whose sympathy for the downtrodden and oppressed frequently leads to his taking the law into his own hands, and his going to jail. His sister Jyoti is an intelligent student who helps her mother and family at home. Jyoti falls in love with a fellow student named Prem, who is handsome and owns a car, but negotiations between the families is made difficult because of Lambu's criminality.
When Prem's family agree to the marriage, Lambu wants his sister Jyoti to have a big wedding, and he concocts a scheme to rob the house of a wealthy man named Seth. Lambu's friend Mahipat Rai (alias Pat Pat) warns him against committing such a crime.
On the night of the planned robbery, the horrendous criminal Chhaganial gets to the house first, where he steals valuable documents and kills Seth. When he arrives and discovers that Seth has been killed, Lambu runs off but shortly afterwards wins the lottery and becomes known as Mr. Lambu. Chhaganial wanted Lambu's lottery wealth, as well as his sister Jyoti, and lays a trap for him using his accomplice the dancer Veera.
The crime unravels when Veera forgets her mission and surrenders to Lambu, but before she can expose the whole crime, Chhaganial kills her, causing Prem to be blamed. Though Jyoti knows that Prem did not kill Veera, she cannot say anything because she has to protect her brother Lambu, something that is expected of siblings in India, as sisters and brothers never betray one another.[6]
