Thousands of years ago, four demons were trapped in a tomb by a powerful sorcerer. These demons threatened mankind, and lived only to conquer and destroy. A group of nomads opens the tomb, unwittingly releasing the demons into present day. The demons, led by Diabolico, seek to reclaim their city and palace, which is now a US city known as Mariner Bay. When defense organization Lightspeed hears of this news, they immediately initiate their emergency plan - to summon five hand picked individuals to utilize their technology to become Power Rangers, and defend the city from the demons' attacks.
The Lightspeed Aquabase is home to cutting edge technology, developed by Angela Fairweather and her team of scientists. The first of their creations were the Rescue Zords, five vehicles which combined into the Lightspeed Megazord, and the Rail Rescues, which combined into the Supertrain Megazord.
When it was decided to add a sixth Ranger to the team, the Titanium Morpher was created. However, its power was proven to be too much for a person to handle, so it was retired. Shortly after, the Titanium Morpher was stolen by Captain Mitchell's disgruntled son Ryan, who used it to get revenge at his dad, but eventually joined the team as the Titanium Ranger, and was given a new Zord, the Max Solarzord.
Diabolico's frustration in failing to defeat the Rangers ultimately led to his destruction, which paved the way for Impus to evolve into Olympius, who restored his mother, Queen Bansheera, to her bodily form. One of her first plans involved sending an asteroid hurling towards Earth. To stop this, the Rangers were given the Omega Zords, five spacecraft which combined to form the Omega Megazord.
At odds with Olympius, Vypra and Loki revived Diabolico, who rejoined the demons. He was defeated by Olympius, and placed under a spell to make him a mindless lackey. The two powerhouses destroyed the Lightspeed and Supertrain Megazords, but were defeated by the newly developed Lifeforce Megazord.
With only the Queen left, she focused her efforts to take over the Omega and Lifeforce Megazords. She successfully destroyed the Lightspeed Aquabase, but both Megazords were destroyed by the Rangers. The Rangers then raided the Skull Cavern, where they imprisoned Queen Bansheera in the demon tomb, restoring peace to Mariner Bay.