Power Rangers Zeo
Power Rangers Zeo begins immediately after the events of Mighty Morphin Alien Rangers, where Tommy and the other Rangers (Adam, Rocky, Tanya, Katherine and Billy) witness the destruction of the Command Center. After recovering, the powerless Rangers discover the Zeo Crystal intact in the rubble—apparently dropped by Goldar and Rito Revolto. The Crystal guides them to a portal, which takes them deep underground to the Power Chamber where they find Zordon and Alpha 5 waiting for them. The Mighty Morphin Power Rangers become the Zeo Rangers, a new team of Rangers powered by the Zeo Crystal. The four remaining Mighty Morphin Rangers, Tommy, Adam, Rocky and Kat become Zeo Ranger V — Red, Zeo Ranger IV — Green, Zeo Ranger III — Blue and Zeo Ranger I — Pink respectively and Tanya Sloan joins the team as Zeo Ranger II — Yellow, while Billy chooses to become their technical advisor rather than continuing as a Ranger.
The Machine Empire, led by King Mondo and Queen Machina, enters Earth's solar system, seeking to conquer Earth, with the Zeo Rangers serving as the only opposition. Many, even Rita Repulsa and Lord Zedd, are forced to flee to the M51 Galaxy under the threat of destruction. Unbeknownst to anyone, Rito and Goldar – now amnesic – are left behind on Earth. They are taken in by Bulk and Skull, who have them serve as butlers. Meanwhile, Bulk and Skull continue to be members of the Junior Police Force until Lieutenant Stone is dismissed, when Bulk tries winning the heart of the chief's daughter. Quitting as a show of respect for Stone, they join him at his new detective agency.
Over time, the Machine Empire wears down the five Zeo Rangers, but they are rescued by the mysterious Gold Ranger. Though his identity is unknown, it quickly becomes clear he is there to help the Rangers. After he is injured in battle, it is revealed that Gold Ranger is an alien, Trey of Triforia. Split into three separate selves, Trey is forced to temporarily pass his powers to a worthy warrior while healing. They attempt to transfer Trey's powers to Billy, but as Billy acquired excess negative energy during the Command Center's destruction, he is unable to do so. The ultimate successor is Jason Lee Scott, the original Red Power Ranger and team leader. This event also sees the introduction of the more powerful Super Zeozords, which were used against a tougher generation of machines. The Super Zeo Megazord is powerful enough to later destroy King Mondo, creating a power vacuum in the Machine Empire.
Secretly returning from the M51 Galaxy, Lord Zedd and Rita seek to become top villains again. Operating out of an RV with Finster, they restore Goldar and Rito's memories, retrieving the pair in the process. After King Mondo's death, they launch their first plan, to use Louie Kaboom to take over the Machine Empire. Though he succeeds, he breaks free of Zedd and Rita's control. He embarks on his own plans to conquer Earth and destroy the Zeo Rangers. Louie is eventually killed by King Mondo's first-born son Prince Gasket and his wife Princess Archerina, who rule until King Mondo's reconstruction is complete and causes them to flee.
When Billy begins rapidly aging as a side-effect of restoring his proper age before undoing Master Vile's spell in the last series, the Zeo and Aquitian Rangers race to help him and fend off monsters from King Mondo as well as Zedd and Rita. Billy leaves Earth for treatment on Aquitar and chooses to stay to be with Cestria. Soon afterwards, it is discovered the Gold Ranger powers are leaving Jason and draining his life force in the process as the alien powers were not meant for a human. Trey is still in recovery, but a risky gamble with the Zeo Crystal heals him, restoring his powers. Rita and Lord Zedd finally get revenge on the Machine Empire by crippling their leaders with a bomb.
good versus evil