The ambitious and imaginative boy, Roland Deschain, haunted by visions of a parallel world, aids its guardian, the disillusioned sorcerer, Walter O'Dim, known as the Man in Black, in preventing the destruction of the nexus of universes, the Dark Tower, by the evil sorcerer, Marten Broadcloak, also known as the Crimson King, who seeks to defeat reality and impose his tyrannical rule on all worlds.