Hulchul (1971)

Peter (O. P. Ralhan) and Kitty (Helen) love each other, but due to Peter's poverty, they are unable to marry each other. One day, during a secret rendezvous, Peter accidentally overhear a conversation between one Mahesh Jetley and his paramour, where Mahesh tells her that he is soon going to bump off his wife on a certain date. Peter and Kitty decide to foil this man's plans. However, there are 2 problems: 1 - They have not seen Mahesh or his paramour's face. 2 - Even if they had, no one would believe their story. Hence, the lovers decide to do a little investigation on their own. They find three Mahesh Jetleys. On some snooping, they find that each man is married and each of them has a miserable married life. To find their suspect, they devise a plan whereby they will stage an attack on each man's wife. Whoever the culprit is, will freak out and his identity will be revealed.