The series takes place in the fictional town of Angel Grove, California. On an exploratory mission, two unwitting astronauts discover an extraterrestrial container (referred to as a dumpster as a result of its stench) and breach the unit, inadvertently releasing the evil alien sorceress Rita Repulsa from 10,000 years of confinement. Upon her release, she and her army of evil space aliens set their sights on conquering the nearest planet: Earth. When the wise sage Zordon becomes aware of the release of the evil which he was responsible for capturing so long ago, he orders his robotic assistant Alpha 5 to select five "teenagers with attitude" to defend the Earth from Rita's attacks. The five teens chosen are Jason Lee Scott , Kimberly Ann Hart , Billy Cranston , Trini Kwan , and Zack Taylor . Zordon gives them the ability to transform into a fighting force known as the Power Rangers, providing them with an arsenal of weapons at their disposal, as well as colossal assault machines called Zords, which can combine into the Megazord.
The series begins with five teenagers combating Rita and her seemingly endless array of monsters, however, consecutive failures lead Rita to adopt a new method for conquering Earth and destroying the Power Rangers: by attacking them with one of their own. Using the Green Power Coin, Rita kidnaps and brainwashes a local teen whose fighting skills prove to equal that of Jason's in a martial arts contest held in Angel Grove. The new teen, Tommy Oliver , passes Rita's tests, becoming the Green Ranger. Entrusted with Rita's Sword of Darkness, source for the continuance of the evil spell he has fallen victim to, Tommy comes dangerously close to defeating the Power Rangers, especially when Rita causes a Solar eclipse that temporarily drains the Megazord's power. However, the Green Ranger is ultimately defeated, and the Sword of Darkness is destroyed by Jason. Now free from Rita's spell, Tommy chooses to use his Green Ranger powers to assist the other Rangers in defeating the evil that gave them to him in the first place. His Zord, the Dragonzord, is reconfigured to enable it to help form more powerful Zord combinations alongside the other Dinozords.
As time goes on, Rita focuses her plans on eliminating Tommy in order to regain the powers that she believes belong to her. Utilizing a special wax touched by Tommy when he was evil, Rita uses a magic Green Candle to sever Tommy's link to the Morphing Grid and slowly remove his powers, returning them to her. In the end, Tommy loses his powers, however, he is able to prevent Rita from reclaiming it by transferring the remains to another Ranger who can operate them based on their own link to the Morphing Grid. Tommy chooses Jason who, feeling guilt for failing to protect Tommy's powers, accepts them. However, Tommy later returns to the team when the other Rangers' Power Coins are handed over to Rita in exchange for their kidnapped parents. With Zordon's help, Tommy regains his Green Ranger powers and successfully retrieves the other Rangers' Power Coins. However, Tommy's regained powers are only temporary and must be frequently re-charged by Zordon, who makes no attempt to hide the fact that the Green Ranger's powers will ultimately fail. Despite this, Tommy remains determined to continue assisting the other Rangers as long as possible.