We start out at what appears to be an underwater mining operation on the planet Rylos. One of the miners is thrilled to have found the Solar Sphere, but joy turns to horror when the great sea monster Leviathan appears. As the people scatter, Leviathan swallows the Solar Sphere and swims off.
Rob and the Orbots are sent to Rylos to deal with the sea monster which is attacking the mining operations. There they meet Torkis, the head of the operation, and Amon, an oceanographer. Knowing that Leviathan has been attacking freight subs, that's where the Orbots wait for him and, sure enough, he attacks. Mighty Orbots and Leviathan battle, but Mighty Orbots is unable to beat him, and he swims off. While the other Orbots clean up the mess left from this last attack, Ohno detects the brain wave machine which we learn Amon is using to control Leviathan. While Rob and the Orbots try to reach its source, we also learn that Torkis is actually working for Shadow, trying to retrieve the Solar Sphere for Umbra to use in his plans of galactic conquest.
Rob and the Orbots catch Amon in his underwater headquarters, and Amon explains that Torkis is not only destroying the balance of nature with his mining, but that he's also working for Shadow. At that point Torkis shows up, having followed the Orbots, and steals the brain wave helmet which was controlling Leviathan. He uses it to get inside Leviathan and search for the Solar Sphere. Mighty Orbots follows him in and, while Torkis retrieves the Sphere, Mighty Orbots takes a trip through Leviathan's body to get to the brain and deactivate the control mechanism. While Torkis prepares to escape on a Shadow space ship, Leviathan, now unconscious, tumbles towards the underwater city below. Mighty Orbots manages to slow him down and divert him, and then attacks the Shadow ship, retrieving both Torkis and the Solar Sphere.