When the evil Skeletor finds a mysterious power called the Cosmic Key, he becomes nearly invincible, seizing Castle Grayskull and the surrounding city. The Sorceress is now Skeletor's prisoner and he begins to drain her life-force as he waits for the moon of Eternia to align with the Great Eye of the Universe which will bestow god-like power upon him. However, courageous warrior He-Man locates the locksmith inventor Gwildor, who created the Key and has another version of it. During a battle, one of the Keys is transported to Earth, where it is found by teenagers Julie and Kevin. Now, both He-Man and Skeletor's forces arrive on Earth searching for the potent weapon.