Pithamagan whirls around four characters. Chithan (Vikram) who is orphaned at a young age, devoid of all human contacts lives on his animal instincts and ekes out a living as a graveyard caretaker.
He seems to exhibit behaviour consistent with autism spectrum disorders. Gomathy (Sangeetha), a petty ganja seller, who pities Chithan’s condition, gets him a job at the ganja fields of the main villain. Sakthi (Surya), the conman, cons Manju (Laila), a polytechnic student but does not get away with it.
Sakthi meets Chithan in jail and takes pity on him and befriends with him. It is Sakthi’s affection that melts Chithan’s stony heart. Later, Sakthi gets into trouble with an influential narcotics dealer and the story moves slowly into a gory and fitting finale.