Deep inside Castle Plun-Darr, the Mutants are showing off their latest creation, a Plun-Darrian Warbot to Mumm-Ra. Slithe demonstrates the robot's abilities by making it turn a nearby Frogdog into statue. Even though Mumm-Ra is not impressed by it, Slithe assures him that the robot has a lot more deadly weapons in its arsenal. He then instructs the robot to head to Cats Lair.Meanwhile at Cats Lair, the ThunderCats are inspecting the Time capsule that they had recovered from the Caveman. The device projects a hologram of Thundera and Lion-O marvels at the beauty of the image. Later that night, Lion-O, who is on watch, decides to try out the Time Capsule himself. When he switches it on, he is standing right in the path of the projector and, as a result he somehow gets transported back in time and space to Thundera, just before the planet's destruction.The approaching Warbot is detected by the Cats Lair's scanners and the ThunderCats all gather in the control room, alarmed at the sight of the approaching behemoth and at the same time wondering where Lion-O is. Panthro fires lasers at the Warbot but it sends the rays back causing the lair's eyes to shatter. Panthro then employs the Ballista to shoot a variety of deterrents at the robot including fire, ice, a missile and a giant chain but the Warbot manages to overcome all of them.Back on Thundera, Lion-O meets his old pet, Kano, a saber-tooth cat who leads him to his father, Claudus. There he sees Slithe and Vultureman trying to force Claudus to give them the plans of the Warbot. Lion-O jumps in and sends theMutants fleeing. Claudus then gives Lion-O the plans of the Warbot, hoping that they might prove useful to him in another world, another time. Lion-O tries to convince Claudus to leave with him but he refuses because he has to stay and boost the guidance system on Jaga's ship. As the planet's earthquakes get worse, Lion-O bids his father farewell and leaves.In the meantime, the Warbot fires huge chains which attach themselves to the Cats Lair's head and pulls out the entire head of the fortress. The robot then jumps onto the lair and fires a grey substance at the ThunderCats which turns them all into statues. At that instant, Lion-O arrives back at the lair and uses the Sword of Omens to free his fellow ThunderCats. He then turns the sword on the robot and pushes it away from the lair. Lion-O shoots out of the lair using the Ballista and lands near the Warbot's feet. As the robot raises its giant foot to crush Lion-O, the young lord inserts his sword into a small red disc on the Warbot's foot. This causes the robot's foot to explode and the entire robot gets destroyed.