Bombay Police are baffled by a sequence of crimes - all by the hands of arch-criminal "Black Cat" who leaves his calling card at each scene of the crime. The Commissioner assigns this matter to this greatest plainclothes agent, Rajan. Rajan's investigations lead him to suspect Professor Gupta, who can also be the brother of his girlfriend, Nita. Rajan decides to make use of Nita's love for him, and spies on Gupta. When Nita finds out, she is enraged at Rajan, and blames the police who she feels are covering-up their inefficiency by making a scape-goat of an harmless man. Rajan fails to show that Gupta is in some way concerned with "Black Cat", and the Commissioner offers him a deadline. If Rajan doesn't apprehend Black Cat inside that deadline, he could also be suspended and even dismissed from the police pressure. With no clues in any respect as to the whereabouts of Black Cat and it is gang, Rajan has the problem of his life, which he might not be capable to fulfill.
