On the planet Eternia, the evil Skeletor and his army of darkness have taken over Castle Greyskull, the mysterious castle, and imprisoned The Sorceress of Greyskull, and Skeletor has begun draining The Sorceress of Greyskull's powers as he bids to claim the powers of Greyskull and become master of the universe. Mighty warrior He-Man, the most powerful man in the universe and his companions loyal soldier Man-at-Arms, his daughter Teela and a dwarf inventor named Gwildor accidentally finds themselves on Earth, by Gwildor's creation, The Cosmic Key, a device that can open portals that lead to any part of the galaxy, which Skeletor requires in his goal for universal conquest. But when the Comsic Key is taken in possession by Julie Winston and her boyfriend Kevin, both unaware Earth is about to become a battleground, as Skeletor and his mercenaries arrives on Earth, as they go in pursuit of He-Man and his companions who are searching for The Cosmic Key so they can return to Eternia and defeat Skeletor.