In Raj Kapoor's own words, Aag is "the story of youth consumed by the desire for a brighter and more intense life." Kewal and Nimmi are childhood sweethearts who share a passion for theatre. They promise each other that when they grow up, they will together start their own theatre company. An unfulfilled dream as Nimmi and her parents move to another town.

Years later, two young men Rajan (Prem Nath) and Kewal (Raj Kapoor) revive an old theatre that closed down. One day, a young destitute girl (Nargis) comes to the theatre and begins to act in Kewal's plays. Fascinated by her, Kewal names her Nimmi. But when he discovers that Rajan is also in love with her, he steps aside only to realize that Nimmi loves him. Kewal gets badly scarred on his face when trying to douse a fire in the theatre. A horrified Nimmi switches loyalties and chooses Rajan. A wedding night, a flower-bedecked bedroom, and the bridegroom turns to reveal a badly burnt face. The bride (Nigar Sultana) screams in shock. The man is Kewal.

Who is the girl?

Will Rajan ever find his beloved Nimmi? And if he does, will she be able to see the real Kewal beyond his disfigured face?

Aag was the debut of Raj Kapoor's astounding career as one of Indian cinema's most illustrious directors and was the first time Nargis and Raj Kapoor came together as a romantic on-screen couple. Though Ram Ganguly was the music director of the film, scoring such haunting numbers as "Zinda hoon is tarah", his assistants were Shanker and Jaikishan. So impressed was Raj Kapoor by their contribution to the film's music, that he vowed to work with them in his next film. The rest as they say is history...