Aasai means desire. The film tells about the desire of Prakashraj towards his sister-in-law Suvalakshmi. He even goes to the extent of murdering his wife. He leaves no stone unturned to attain her. He creates a rift between her and her heartthrob Ajith Kumar. He gains the confidence of his father-in-law. How Ajith saves his lover from Prakashraj's clutches is the rest of the narration.
