Prince Adam is the young son of Eternia's rulers, King Randor and Queen Marlena. Whenever Prince Adam uses the Sword of Power by holding it aloft and saying the magic words "By the Power of Grayskull, I HAVE THE POWER" he is transformed into He-Man, the most powerful man in the universe. Together with his close allies, Battle Cat, The Sorceress, Teela, Man-At-Arms and Orko, He-Man uses his powers to defend Eternia from the evil forces of Skeletor. Skeletor's main goal is to conquer the mysterious fortress of Castle Grayskull, from which He-Man draws his powers. If he succeeds, Skeletor would conquer the world of Eternia, and possibly the whole universe.
While everybody else is preparing for his and Princess Adora's birthday, Prince Adam is helping Man-At-Arms finish up the Sky Spy, a space shuttle intended to spy on Skeletor. The moment they head back to the castle, though, Orko gets inside the ship and messes around with the controls, causing the ship to blast off into the sky with him in it. Skeletor catches sight of the aircraft and, despite not knowing what it is or who is flying it, he gives chase after it in the Collector. Before he can take it down, He-Man and She-Ra, who are also unaware that Orko is in the Sky Spy, show up and punch a hole in the Collector, throwing it off course.
This special is a compilation of three episodes (""Day of the Machines"", ""The Cat and the Spider"" and ""Trouble in Trolla""), linked together within a wraparound sequence in which Skeletor narrates to the viewer his failures to conquer Eternia. It was put together to promote the show's second season.