Bill Skarsgård stars as "Boy" who vows revenge after his family is slaughtered by Hilda Van Der Koy, the deranged matriarch of a corrupt post-apocalyptic dynasty that left the boy orphaned, deaf and mute. Driven by his inner voice, one which he chose 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 rebels. Chaos ensues as Boy commits bloody martial arts mayhem, inciting a wrath of butchery and bloodletting. As he tries to get his bearings in this rambling realm, Boy soon falls in with a desperate resistance group, all the while squabbling with the apparent ghost of his rebellious little sister.