Discovering an underground river in the caverns deep beneath Snake Mountain, King Hiss sends his minions Rattlor and Tung Lashor on a raft voyage to learn where it leads. They find that the river flows through a long-forgotten tunnel beneath Castle Grayskull. Hiss is quick to capitalize on this amazing discovery, and leads an attack on the ancient fortress. Paralyzing a sleeping He-Man with a few drops of venom, the Snake Men drag their captured enemy back with them through the tunnels, not realizing how quickly their poison is wearing off. Fully regaining his faculties during the long raft ride back to Snake Mountain, He-Man is more than a match for Hiss and his army, and in a terrific battle, puts an end to their scheme. Sailing back towards Castle Grayskull, He-Man gives a mighty shout, causing an earthquake to effectively seal the underground cavern, never to be used again by the forces of evil.
(A good story where the Snake Men are depicted as strong and competent; however, Skeletor and his minions never make an appearance, and Snake Mountain is referred to as the stronghold of the Snake Men!)