The Arsonist involves the struggles of an undocumented immigrant family and a boy's coming-of-age. The son Kesuma must forge his own identity against the intimidating presence of his father Kakang, a man proud of his Javanese heritage and well aware of the social inequalities that allow his exploitation. Kakang counteracts by torching the property of those who slight him, leaving Kesuma simultaneously proud, fearful and ashamed. A clash of wills is all but inevitable. The film climaxes in a poignant conflagration, literal and metaphorical.

Os fails in his examination and his looked down upon by his family and the villagers. Nevertheless he is good in the chemistry and biology and invent a formula that enables mutes and animals to speak. A businesswoman is interested in his invention and brings him to Kuala Lumpur. Unfortunately, she cheat him and he is declared bankrupt.