Mohan is a young man who lives with his widowed mother, is in love with a young woman named Shyama, and both would like to get married. Unfortunately, before that could happen, Shyama is shot dead, the police get involved, an eye-witness named Bindiya names Mohan as the killer, as such Mohan is arrested, tried in Court, found guilty and sentenced to be hanged. The only one who believes in Mohan's innocence is his mother, Gangadevi. She advertises in the newspapers offering a reward of Rs.10,000/- to whoever can prove her son innocent, asking readers to direct their responses to Post Box 999. No one ever responds, until after 5 years when a Reporter, Vikas, of "Prakash" publications comes across the ad and decides to prove Mohan innocent. Assisting him are Gangadevi and a young woman named Nilima, eventually both Nilima and Vikas fall in love. Their investigation take them to a variety of people, including Banarsilal, Bindiya who witnessed the killing, and a killer named Shamsher Singh...