Nastik is an action revenge drama. The movie follows the story of a young man named Shankar (Amitabh Bachchan), who is devastated when his entire family is killed by a criminal named Tiger (Amjad Khan). He grows up to become an atheist, as he blames God for his misfortune and now, has no trust in God. He trains himself to fulfil the only mission of his life, which is to avenge the death of his entire family and finish Tiger. Will Shankar succeed in his mission?