With the peace talks between the Speleans and the Caligars having broken down, King Randor, Prince Adam, and Man-At-Arms journey to Subternia to help them reach a settlement. At the same time, the Evil Warriors decide to attack Castle Grayskull form below as all of their other methods have thus far failed. It is not long before the two groups meet in the depths of Eternia...

All of Eternia is put on high alert when Kobra Khan escapes from the Royal Palace prison compound. The Masters journey to the Mystic Mountains where they inform the mysterious Zokak of the situation. Skeletor is quick to employ the talents of Kobra Khan, unsuspecting of the Snake Man's intent on releasing his ancestors from a hidden void in Snake Mountain...

Desperate times call for desperate measures; in an effort to prevent the return of the Snake Men, the Masters of the Universe seek a temporarily alliance with the Evil Warrirors. Skeletor agrees to join his forces with theirs, but then ambushes the Masters when they arrive. With the Masters and the Evil Warriors preoccupied by their own battle, Kobra Khan and Rattlor are able to make their way to the Void within Snake Mountain, freeing their ancestral allies: Tung Lashor, Sssqueeze, Snake Face, and the leader of the Snake Men, King Hssss!

Having seized control of Snake Moutnain, the Snake Men now seek the power of the Elders. Allying herself with King Hssss, Evil-Lyn reveals that the power he seeks lies within the walls of Castle Grayskull. He-Man and Zodak arrive just in time to witness King Hsss and Evil-Lyn using their combined powers to enter the castle! He-Man battles the hordes of Snake Men and Zodak confronts King Hssss, who has poisoned the Sorceress with his deadly venom...

The Masters of the Universe learn from Lord Dactys that King Hssss and his Snake Men are alive and well and are attempting to retrieve the powerful Serpent's Ring from the Sea of Rakash. Immediately, the Masters set off in pursuit, catching up with King Hssss and his henchment at the village of Felis Folia. With the Serpent's Ring now in his possession, King Hssss has already transformed the villagers into Snake Men, and does the same to the Masters when they arrive. It is up to He-Man, Roboto, and Orko to stop King Hsss form turning everyone on the planet into snakes!