The ThunderCats go on the offensive, but Mumm-Ra won't see his lizard army crushed so easily. He tasks Slithe with recruiting two new and vicious Generals.
Tygra and Lion-O enter the Astral Plane to retrieve the stone, but encounter Mumm-Ra in the process. Grune and Panthro have their final duel. Cheetara finally chooses her beau.
The Cats are ready to retrieve the stone from the "Astral Plane" in the Elephant Village, but find it overtaken by Grunea and Mumm-Ra's forces. Plus, Tygra and Cheetara's early relationship to one another is revealed.
Panthro finally joins the team, but his gruff demeanor intimidates Lion-O. Despite his best efforts, Panthro can't dissuade the Cats from following him on a mission to get Thundrillium to fuel the Thundertank.
The ThunderCats' search for the Tech Stone leads them high above Thundera to the floating bird city of Avista, where the stone is the power source for their city.
While hiding from the unstoppable lizard army, Lion-O encounters a race of creatures who live out their entire lifetime in 24 hours, and learns a valuable lesson about hope.
Thundera is attacked by lizards who have acquired salvaged ancient technology. In face of betrayals, revelations and tragedies, Lion-O and Tygra mount a rescue with the team.
While traveling, Lion-O's cockiness loses him the Sword of Omens to the Duelist, a villainous sword-collector. With the help of the listless Drifter, Lion-O must get it back.