The ThunderCats accompany Panthro to Cloud Peak Mine to search for Thundrilium for the Thundertank. Along the way, Panthro and Grune's past is explored, from their first encounter to the reason behind Grune's betrayal.

Cast: Will Friedle, Troy Baker, Clancy Brown, Emmanuelle Chriqui, Robin Atkin Downes, Larry Kenney, Matthew Mercer, Kevin Michael Richardson