Nagina is a story about Rajiv, who as a kid is bitten by a snake while roaming in the forest. A snake charmer named Bhaironath manages to save his life by killing the snake.
Years later, Rajiv returns from London where his mother wants him to get married to Vijaya. However, Rajiv comes across a beautiful orphan named Rajni and falls in love with her. Despite his mother's objections due to Rajni's orphan status, she later agrees for their marriage.
Rajiv and Rajni get married and are living happily until Bhaironath arrives and reveals to Rajiv's mother that Rajni is actually a shape-shifting snake seeking revenge for the death of her lover, who had bitten Rajiv in childhood. However, Bhaironath's true intentions are to capture Rajni, as she knows about a hidden pearl that can make him powerful.