Thanaha portrays the story of two friends Vishnu and Roy who end up in the Police service after the death of their fathers. What follows is how Vishnu and Roy unravel the mystery behind the case of a missing culprit.

The new superintendent of prisons, who is new to his post, first finds out about the suicide attempt of a young man named Christy, who was convicted of murder for seven years. Christie, who lost his parents at a young age, had only a few friends with him and then a girl named Daya whom he sincerely loves. But she never recognized his love. Christie now knows that she's engaged to be married to someone else. Thus he attempts suicide. Resulting conflicting events form the crux of the movie "KAMMAL".