Mohabbat Aag Si is the story of Aapa Ji who is revered by everyone around her because she is considered to be one of those pious personalities who can change people’s life only by saying a prayer for them. Aapa Ji spends her days clad in a white dress busy in prayer all day long but at night time Aapa Ji is a completely different person. Sharifa the maid, is Aapa Ji’s friend and confidant, she is the only one who knows all of Aapa’s secrets but still respects her and is very faithful.

Aapa Ji lives with her brothers Sharafat and Wajahat. Both brothers are indebted to Aapa Ji and hold great respect for her because she brought them up. Aapa considers the wives of his brothers as a "threat" and “competition” and she makes sure that her brother Sharaft and his wife Samia do not have any children.
Will the brothers ever find out Aapa Ji's true identity? Will her sisters in law accept Aapa’s position in the house without revolting against her?