1890s, Dakota Territory. A Lakota Indian's tribe is slaughtered while escaping the reservation, though the youth is spared by one of the pursuing soldiers who happens to be his estranged father. Wandering the plains, the Lakota is seduced by a tree-like alien parasite that promises purpose and revenge against the Americans in exchange for helping it spread across the land through human sacrifice. Meanwhile, his father and half-brother's infantry squad is tasked with tracking down and killing him.