While on a peace mission in Subternia, He-Man, Man-At-Arms, and King Randor must prevent Skeletor, Evil-Lyn, Beast Man, and Whiplash from attacking Castle Grayskull from below.
A simple chess-playing robot named Roboto helps the Masters of the Universe battle an evil army of skeletons created by Tri-Klops much to Teela's frustration.
After witnessing the damage inflicted on the palace by Keldor (now calling himself Skeletor due to his horrific appearance), Adam embraces his new destiny as He-Man, defender of Eternia. Meanwhile, the Masters search for King Randor and are caught in their first battle against the Evil Enforcers.
After years of imprisonment behind a Mystic Wall, Keldor (now Skeletor) and his minions escape to seek revenge and power.
Tired of being thought a coward, Adam tries to show he can be just as much a hero as He-Man and winds up Skeletor's prisoner.
To prevent Skeletor's Serpintaurs from attacking the newly-formed Eternian Council, the Masters end up using special dragons to help defend them.