"Boy" (Bill Skarsgård) vows revenge after his family is murdered by Hilda Van Der Koy (Famke Janssen), the deranged matriarch of a corrupt post-apocalyptic dynasty that left the boy orphaned, deaf and voiceless. Driven by his inner voice, one which he co-opted from his favorite childhood video game, Boy trains with a mysterious shaman to become an instrument of death and is set loose on the eve of the annual culling of dissidents.

Bedlam ensues as Boy commits bloody martial arts mayhem, inciting a wrath of carnage and blood-letting. As he tries to get his bearings in this delirious realm, Boy soon falls in with a desperate resistance group, all the while bickering with the apparent ghost of his rebellious little sister.