

Lion-O wants to prove to the ThunderKittens that he's not just some boring old adult like Tygra, even if it means ignoring his instincts and messing with an obviously evil crystal.
Fleeing the destruction of their home planet Thundera, Lion-O and the ThunderCats land on the world of Third Earth. But their enemies, the Mutants of Plun-Darr have followed them and it turns out Third Earth already has a Mumm-Ra problem.
Fleeing the destruction of their home planet Thundera, Lion-O and the ThunderCats land on the mysterious, dangerous, all-around awesome world of Third Earth! But their enemies, the Mutants of Plun-Darr have followed them and it turns out Third Earth already has a Mumm-Ra problem - can Lion-O learn the ropes of being a leader in time?