Lion-O is haunted by the recurring nightmares of Thunderians being killed on Thundera while he fled to the safety of Third Earth with Jaga and the other ThunderCats. Jaga later tells Lion-O that 3 more Thundercats have, in fact, survived and are also living on Third Earth. The ThunderCats decide to search for the 3 new Thunderians, but Mumm-Ra has plans as well and takes the new Thunderians as his prisoners to Fire Rock Mountain.
