Two astronauts are exploring the moon and happen to come across a space dumpster. When they open it, witch Rita Repulsa and her minions Goldar, Squatt, Baboo, and Finster emerge from a 10,000-year captivity. Rita decides the time has come to conquer Earth and rebuilds her palace on the moon, from which she can launch her attacks.
In the city of Angel Grove, California, Jason Lee Scott, Zack Taylor, Billy Cranston, Trini Kwan, and Kimberly Hart are hanging out at Ernie’s Youth Center. The guys are working on karate, while the girls are practicing gymnastics. Farkus Bulkmeier and Eugene Skullovitch, better known as Bulk and Skull, come to harass them but make fools of themselves.
The five teens are later sitting down to some fruit shakes from Ernie’s Juice Bar when an earthquake begins. At that moment, in the Command Center, Zordon, the wise sage who battled Rita many millennia ago, tells his robotic assistant, Alpha 5, to bring him five "overbearing and overemotional humans" (a.k.a. teenagers) to fight Rita.
The five teens are then teleported from the Juice Bar to the Command Center, where Zordon explains the situation and declares them as the first Power Rangers, each with a powerful Zord. Jason, dubbed leader of the team, becomes the Red Ranger, with the power of the Tyrannosaurus; Zack is made the Black Ranger, with the Mastodon; Billy becomes the Blue Ranger, with the Triceratops; Trini is made the Yellow Ranger, with the Saber-Toothed Tiger; and Kimberly becomes the Pink Ranger, with the Pterodactyl.
The teens don’t buy into it at first and leave the Command Center. At that moment, Rita sends a squad of her new Putty Patrollers to attack them. At first the Putties succeed, but the teens morph into the Power Rangers and beat the Putties. Then they are sent back to Angel Grove to fight more Putties, along with Rita’s most powerful warrior, Goldar.
The Rangers maintain the upper hand until Rita throws her magic scepter to Earth to make Goldar giant. In response to this, the Rangers summon the Dinozords and combine them into the Megazord for the first time. Goldar has the upper hand on them at first, until Jason calls on the Power Sword. Afraid of being destroyed, Goldar retreats to the safety of Rita’s palace, where the angry sorceress harshly reprimands him.
Back at the Command Center, the teens are finally convinced that they can save the world from Rita’s evil, and they agree to the following rules: (1) “Never use your power for personal gain”; (2) “Never escalate a battle unless Rita forces you to do so”; (3) “Keep your identity secret.” Zordon promises that he will be there to advise them whenever they need it, and thus the first team of Power Rangers comes together to save the world.
In the Youth Center, Kimberly is trying to write a song. Kimberly asks Zack if he can help her with the lyrics. This gives Lord Zedd the idea to create Guitardo. The following day, Tommy, Billy, Jason, Zack, Kimberly, and Trini are in the park having a picnic. Richie drives by on his bike. Trini invites him to join them, but Richie can't as he is helping his mom unpack. Meanwhile, Bulk & Skull are working on their newest idea to reveal the identities of the Power Rangers. Skull is dressed like a princess and Bulk a dragon. Bulk & Skull hope to lure the Rangers by pretending the "princess" is being attacked by a "dragon". Skull protests about being the bait and Bulk talks him into by declaring he would make better bait than Skull. Bulk & Skull put their plan into action and Bulk starts chasing Skull around. Billy, Jason, Zack, Kimberly, Trini, and Tommy hear screaming and race off to investigate. Jason, Zack, Kimberly, Trini, Tommy, and Billy discovered the screaming is coming from Bulk & Skull. Bulk & Skull tell them to leave and Trini tells them they shouldn't cry wolf. Bulk & Skull think Trini's confused, as there are no wolves in Angel Grove. Jason, Zack, Billy, Tommy, Kimberly, and Trini leave. Bulk & Skull continued with their plan, until Skull becomes tired and wants to rest. Bulk tries to take off his helmet, but he can't. Guitardo appears and chases Bulk & Skull. Meanwhile, the alarm has gone off in the command center. Zordon tells Alpha 5 to contact Zack, Billy, Tommy, Kimberly, Trini, and Jason. Zordon tells them there is a monster in the park, but they must teleport to the command center first. Zordon has Alpha 5 check out Tommy's powers, while the rest are fill in on the monster's ability to hypnotize people. Kimberly is outraged that Guitardo is using her guitar.
Alpha 5 tells Tommy that he doesn't have much of his powers left. Zordon tells Tommy he has to stay behind. Kimberly protests, asking if there isn't a way they can power up Tommy like before. Unfortunately, this is no longer an option. Kimberly, Jason, Trini, Zack, and Billy are all concerned for Tommy. They power up and head into the park where they confront Guitardo. Before the Rangers can even battle Guitardo, Guitardo starts playing his music. Guitardo soon has Black Ranger floating up in the air and under his control. Guitardo quickly sends Red Ranger, Yellow Ranger, and Blue Ranger floating as well. Pink Ranger does her best to resist Guitardo hypnotic guitar playing. In the command center, Tommy watches the viewing globe. Tommy insists on going to help his friends and Zordon lets him. Green Ranger arrives to help Pink Ranger. Green Ranger battles Guitardo and Guitardo leaves, telling them to find him on the fair grounds. Green Ranger and Pink Ranger contact Zordon, who tells them the only to help their friends is to destroy Guitardo. Green Ranger had Pink Ranger guard the rest of the Rangers, while Green Ranger goes to the fair grounds. Pink Ranger contacts Alpha 5 and tells him to keep an eye on the rest of the Rangers, she is going to help Green Ranger. Green Ranger arrives at the fair grounds and soon battles Guitardo.
Guitardo tries to take control of Green Ranger. Green Ranger discovers by playing his flute, he can stay in control. Pink Ranger arrives to help Green Ranger. Pink Ranger tells Green Ranger they have to fight music with music, which Green Ranger had already figured out. Pink Ranger plays a harp and then using Green Ranger's dagger, destroy Guitardo. The rest of the Rangers land on the ground and they are okay. Green Ranger tells Pink Ranger that she has saved them all. Later, a rain storm hits Angel Grove, and Kimberly, Billy, Zack, Tommy, Trini, and Jason bring the picnic indoors to the Youth Center. Bulk & Skull stumble in, Bulk is still having problems removing his helmet and asks for help. Trini tells them they will help them, if they promise not to cry wolf anymore. Bulk & Skull cross their fingers behind their backs and promise. Billy gets up, and turning counter clockwise, manages to remove the helmet. Bulk plans the whole idea on Skull, while Skull tells Bulk he never gets to plan anything. Bulk & Skull walk out. Zack, Kimberly, Tommy, Billy, Trini, and Jason all laugh. Zack comments if only Bulk & Skull knew. Tommy tells them he is going to miss this. Kimberly tells Tommy she has written a song. Kimberly plays her guitar and starts to sing, with Zack joining in. After the song, Tommy tells them he doesn't know what to say. Kimberly tells Tommy that he doesn't have to say anything. They all put their hands within a circle and make the promise, forever.