Original Airdate ?/?/1983
Man-At-Arms and Prince Adam are flying back to the Royal Palace when the Wind Raider's engine stops. Adam transforms into He-Man, then latches the Wind Raider's grappling hook to a mountainside saving them from disaster.
Back at the Royal Palace, He-Man feels as if the Wind Raider is getting heavier and heavier. Man-At-Arms concludes that there is a low level of oxygen in the air, that somehow Eternia's oxygen supply is being depleted. When He-Man finally reaches the castle on foot he is shocked to find the jaw-bridge wide open and the castle unprotected.
The Sorceress has a theory about the Sea of Eternia, and a possible water cut-off. He-Man heads for the Mystic Mountains but a band of insect people attack him. The insect leader Garth is worried about the oxygen affecting their species eggs hatching. He-Man and Garth head out to the Sea of Eternia, and encounter Tri-Klops and Beast Man on their way.
They confront Skeletor who is sitting atop his machine, which pumps the seawater into a dammed pit. Garth sacrifices himself, but emerges from the seawater transformed. Skeletor leaves as He-Man destroys the dam foiling Skeletor's plan.
Synopsis by Zadoc Angell