 Calcutta-based Naval Officer Shankar Choudhry lives a wealthy lifestyle with his doctor dad, and mom. One day while returning home in a cab home from a Club, he comes an injured man, Shekhar, takes him home, has his dad nurse look after him, as well as goes to his home to notify his sister, Neela. Both Neela and he fall in love with each other. When Shekhar recovers, he returns home, and it is then that Shankar notices a change in Neela. When he questions her, she refuses to answer. Then Shekhar is shot and killed in his apartment. A Police Dectective Officer assigned to this homicide - has a lighter with the word  S  engraved on it. This leads him to suspect three persons: One is a gangster named Shyam Sunder, second a delinquent runaway child, Sushil Kumar alias Daaku, who lives with his maternal uncle and aunt; and the third is none other than Shankar Choudhry himself.