On the war-torn planet of Eternia, the mystical Castle Grayskull has been taken over by the evil warlord Skeletor, who has imprisoned The Sorceress of the castle and is slowly draining her powers,...

On the war-torn planet of Eternia, the mystical Castle Grayskull has been taken over by the evil warlord Skeletor, who has imprisoned The Sorceress of the castle and is slowly draining her powers, which will be bestowed upon himself when the Great Eye of the Galaxy opens, along with the power which will enable him to become Master of the Universe. While fighting Skeletor's soldiers, the planet's defender, He-Man, and his comrades Man-At-Arms and Teela, ally with a dwarf called Gwildor, who was the unwitting cause of Grayskull's defeat when he mistakenly gave a Cosmic Key to Skeletor's sorceress Evil-Lyn. The key enabled her to enter Grayskull! The heroes manage to sneak into Grayskull, but are quickly overpowered by Skeletor's warriors. Gwildor manages to teleport them to safety with a replica Cosmic Key... but he teleports them to Earth, millions of miles from Eternia, and the key is lost when they land! The Cosmic Key is picked up by two teenagers called Kevin and Julie, who think it is a musical instrument. When Skeletor sends a group of bounty hunters to Earth to capture the key and He-Man, Kevin and Julie find themselves caught up in the intergalactic struggle. Can the heroes get back to Eternia in time to free The Sorceress and save the universe from Skeletor? Or will Skeletor absorb all the power he needs to wreak havoc throughout the entire universe?!