Orko is left to guard Central Tower by himself while the others fix the track. Skeletor arrives in the Fright Fighter, confines Orko, and changes his appearance to look like the Trollan.
He then makes the Fright Fighter invisible. When the others return, he gains their trust. Mysterious accidents begin to occur, and the Sorceress warns them that everything is not what it seems to be (in her usual cryptic talk).
The truth finally is revealed when "Orko" lifts his hat to scratch his head, tipping off He-Man (since Orko never takes off his hat for anyone -- well, except for Dree-Elle).
Anyway, Skeletor changes to his familiar form and gets in the Fright Fighter, intent on attacking Central Tower. He-Man counterattacks in the Blaster Hawk, and ends up shooting down Skeletor.
Skeletor then creates a mud monster, which He-Man destroys as well. It ends with Skeletor retreating, like always.