After failing to impress Skeletor with his latest plan, Tri-Klops decides to overthrow Eternia himslef. It is not long before a near-indestructible army of Bone Monsters are making their way towards the Royal Palace! With the odds stacked against them, He-Man and Sy-Klone defend Eternia as Man-At-Arms latest creation, Roboto, a strategic chess-playing robot, attempts to convince Teela that he can aid them in their battle...