Thanthiran movie is set in the backdrop of tantric arts, yoga and mysticism, the film revolves around a mysterious saint Aacharya Suryadharman (Siddique), who wants to increase his supernatural powers by mantras and poojas. He resides in a fearful, lonesome mountain called Vikramashila. While he is set to perform a special pooja to gain more powers, he has some unexpected visitors: Kiran (Aravinder) and his fianc�e Swethamukhi (Shwetha Menon). Kiran, a BBC reporter, wants to investigate the continuing relationship of Acharya with mystic powers, while Swethamukhi is in search of her long-lost brother. Suryadharman agrees to locate and bring back her brother with the help of his magical manifestations, but in turn proposes to use Swethamukhi, a virgin, to complete his poojas. What happens next is the rest of the story.