Narkasur, a demon king, prays to Lord Bhramha; and gets a boon not to be defeated by the Devas. Hence, he goes to Indra's mother and takes away her symbolic ear rings saying that he can only give it back if he is conquered by Devas. The Devas go to Lord Bhramha and Bhramha says that he has given a boon not to be conquered by Devas but not by Humans. Hence, they can seek help of Krishna. He will do the job for them.
Indra seeks help from Krishna and meets him. Krishna promises to help him. Satyabhama wants to go with Krishna to help him! Krishna agrees.
Krishna and Satyabhama reach the kingdom of Narkasur. Narkasur says that who so ever has come to his kingdom will get death.
An intense fight goes on between Narkasur and Krishna. Narkasur is killed and the ear rings of mother of Indra are got back. Hence, Satyabhama and Krishna set for Swarg Lok.
See it astonishingly presented in Krishna serial by Ramanand Sagar.