Blackmail (1973)

Kailash, the manager of a power plant, is in love with Asha, the daughter of a wealthy businessman, while Kailash's uncle, a scientist, develops a new solar-powered energy formula that could make him and Kalash very wealthy people. Meanwhile, Asha's greedy fiance, Jeevan, plots for Asha to marry Kailash with the help of Asha's unsuspecting father, so that he can weave a plot of misunderstandings and finally obtain the formula to sell it to an international gang.