Hitting our screens in 1996 (for 50 episodes) Power Rangers Zeo begins immediately after the events of Mighty Morphin Alien Rangers, where Tommy, 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. They use the Zeo Crystal to upgrade from Mighty Morphin Power Rangers to the Zeo 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. Billy chooses to become their technical advisor rather than continuing as a Ranger.’
Throughout the series the Zeo Rangers battle The Machine Empire, led by King Mondo and Queen Machina, a force so deadly that Rita Repulsa and Lord Zedd run away from them and leave the galaxy. Rito and Goldar remain on Earth but are now amnesic are 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.
As their battle rages on the Machine Empire wears down the five Zeo Rangers, and just as all seems lost 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.
With King Mondo out of the way Lord Zedd and Rita return along with Finster. They restore Goldar and Rito’s memories, retrieving the pair in the process.
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.
The series used footage from the Super Sentai series Chōriki Sentai Ohranger.