Mumm-Ra and the Mutants plot to open the Time Warp Prison and release the evil Princess Ta-She in order to use her deadly Doomgaze against the Thundercats.

An evil hunter lands on third earth in search of prey to hunt. His holographic machine can tell him about all of the Thundercats, including their strengths and weaknesses, and he is able to hunt down each one of them and put them in Thundrainium cells. He captures all of them but Lion-O and Snarf. Jaga warns Lion-O about Safari Joe before he sets out to save his comrades, and Lion-O is able to defeat him and release his friends.

Vultureman summons Ratar-O to take him to the planet of the Snarfs to capture one of them and use it as ransom with the Thundercats. Snarf, thinking his entire race was wiped out when Thundera blew up, finds out that they have captured Snarfer, his little nephew. The Thundercats set out to find the Mutants and save Snarfer. After successfully saving Snarfer, the Thundercats are faced with the problem of returning Snarfer to his planet. Panthro cleverly invents the Feliner, a spaceship. In order for it to work, though, the machine need a hyperspace mega-condenser. Snarf reminds him that there is one on Ratar-O's Ratstar. The Thundercats once again pursue the Mutants to the wreckage site of the Ratstar to take their mega-condenser.

Vultureman summons Ratar-O to take him to the planet of the Snarfs to capture one of them and use it as ransom with the Thundercats. Snarf, thinking his entire race was wiped out when Thundera blew up, finds out that they have captured Snarfer, his little nephew. The Thundercats set out to find the Mutants and save Snarfer. After successfully saving Snarfer, the Thundercats are faced with the problem of returning Snarfer to his planet. Panthro cleverly invents the Feliner, a spaceship. In order for it to work, though, the machine need a hyperspace mega-condenser. Snarf reminds him that there is one on Ratar-O's Ratstar. The Thundercats once again pursue the Mutants to the wreckage site of the Ratstar to take their mega-condenser.

Mumm-Ra finds out that the Kingdom of Webs has a new Queen, Spidera. Mumm-Ra thinks he can lure Lion-O into her lair. He transforms into a diamond fairy and casts a spell on Lion-O. Snarf follows them and gets trapped in the Kingdom of Webs. Lion-O tries to save him but ends up having to call the other Thundercats. Eventually they confront and beat Spidera.

After the Mutants fail to ambush and defeat the Thundercats with Vultureman's new Thundrainium cannon, Vultureman, furious about the failed attempt and the loss of his weapon, activates a self-destruct built into each of his inventions or repaired machinery, and all the Mutant technology disintegrates. To even the odds, Slithe asks Mumm-Ra to send an electrical energy creature to destroy all the equipment in Cats' Lair, which also seals up the door to the Sword Chamber, trapping the Sword of Omens inside along with all the Thundercats' weapons. The Mutants attack, and manage to capture Cheetara and Panthro. Snarf must climb into the ventilation shafts to reach the Sword Chamber from within, but Jackalman follows him, trying to capture him. Outside, Lion-O is attacked by Slithe and Monkian, and later Mumm-Ra. After Snarf successfully gets the Sword back to Lion-O, Lion-O frees Panthro and Cheetara and they defeat Mumm-Ra and the Mutants.

When a big storm hits Third Earth, the Thunderkittens are trapped in an old space capsule. Meanwhile, Tygra and Cheetra almost crash the Feliner, but Lion-O guides them in for a safe landing with the eye of Thundera. The kittens are captured by Mumm-ra, but end up saving the day by showing him his reflection in the window of the capsule.