The story of "Ek Deewana Tha" follows the life of Shammi, played by Arjun Bijlani, a simple and straightforward man whose life takes a dramatic turn when he falls in love with a woman named Tunoo. As Shammi's obsession with Tunoo grows, his perception of reality begins to distort, leading him down a path of madness and chaos. The series masterfully weaves together elements of romance, drama, and thriller, keeping viewers on the edge of their seats.

The story begins with a couple, and Vinita , visiting Vinita's mother, Pushpa , to surprise her. The narrative quickly shifts as Harish becomes intensely attracted to his mother-in-law after seeing her in a "sultry avatar".