Mathimaran an emotional thiller movie about Nedumaaran a dwarf who is travelling from Tirunelveli to Chennai in search of his loving sister Madhi. At that time Chennai police deals some crucial cases of missing and homicides. During the search of Madhi, Nedumaran reminded his past sad life after madhi elope with her lover. Nedumaaran met his sister madhi with the help of his college days love affair Prabhavathy who is working with the crime team. Nedumaaran wants to become a postman like his father Sundharam (MS Bhaskar). After met his sister madhi, Nedumaaran wants to leave Chennai due to joining his postman work. But some unavoidable situation Nedumaran has to find the neighbour house girl Banu, who is been missing, Nedumaran takes an oath to Banu's parents to find her. Then Nedumaran finds Banu or the killer? And again he enjoyed his life as a postman with her sister madhi?