The film opens in the Cenozoic Era on Earth. A great battle has just taken place. The Yellow Ranger is crawling to safety and de-morphs before she dies. The Red Ranger, Zordon (Bryan Cranston), is the sole survivor of his team. The Green Ranger, Rita Repulsa (Elizabeth Banks), is seeking out the Zeo Crystal to have dominion over the world.
Rita offers Zordon a chance to join her, but he refuses. A huge blast then goes off, sending Rita into the ocean along with her power coin. It's the present day in a small town called Angel Grove. Star football player Jason Scott (Dacre Montgomery) and his buddy are sneaking a cow into the locker room of another school as a prank. The police then arrive on the scene, forcing the guys to flee. Jason drives away recklessly and ends up getting into a pretty bad car accident as his car flips over. Several weeks later, Jason is forced to attend weekend detention classes for the rest of the school year, and he must also be under house arrest.
His father Sam (David Denman) is disappointed in how Jason threw his prospects away and that he has to spend time with other degenerates. When he gets there, he sees Billy Cranston (RJ Cyler) organizing his pencils by color. A bully (Wesley MacInnes) comes over and starts messing with Billy by breaking one of his pencils and calling him a freak. Jason steps in and defends Billy. The bully tries to swing at Jason but he gets smacked hard across the face before being told to not bother either of them again. Kimberly Hart (Naomi Scott) leaves the room before their session begins. She goes to the ladies room where she meets up with two of her old friends, Amanda (Sarah Grey) and Harper (Morgan Taylor Campbell). They have decided to kick Kimberly off the cheerleading squad, and out of their own lives completely.
Harper spitefully cuts Kimberly out of a picture of them before leaving. Kimberly takes the scissors and starts to cut her own hair. After the session is done, Billy catches up with Jason and thanks him for defending him against the bully. He invites Jason to hang out, but Jason shows him the tag on his leg. Billy offers to take it off if he goes to his house. Jason instead goes home, but after hearing his parents arguing about him, he rides his bike to Billy's house. With four minutes left, Billy calmly and carefully removes the tag. He then asks Jason for a favor for himself.
The guys go by a hill where they carry a big crate of equipment that Billy wants to use in a specific location. Jason isn't comfortable with the task and he leaves. He runs into Kimberly, who is swimming in the lake. Meanwhile, another Angel Grove student, Zack Taylor (Ludi Lin), is watching the new girl, Trini (Becky G), doing yoga nearby. Jason and Kimberly talk about the prospect of running away and starting new lives.
Billy works on his experiment and causes an explosion on the side of the hill. Everyone runs to the scene. Zack and Trini meet the other three kids. On the wall are what appear to be different colored gems. Zack breaks them off. They are actually power coins with the colors red, blue, black, yellow, and pink. When they hear alarms going off, the kids run for it. Jason and Billy take Billy's mom's van before going back to get the other three.
Their path is headed in the same direction as an oncoming train. Billy thinks he can make it before the train comes, but the train slams right into the van. The van crashes, and the coins start glowing. Somewhere over the ocean, Sam, who works as a fisherman, has his men pull up a big pile of fish as a storm starts hitting. He discovers Rita's corpse among the fish.
The kids all wake up in their rooms, miraculously unharmed and with enhanced strength (Jason breaks off a piece of his sink and Kimberly crushes her phone in her hand). They still have their power coins on them. At school, the bully goes up to Billy and tries to break his wrist, but Billy's bones don't budge. The bully then headbutts Billy, only to get knocked unconscious and have all the kids think Billy did it on his own. He meets up with Jason and Kimberly, who decide that they should go back to the hill to investigate what is happening to them. The three return to the hill and find Zack trying to break through the wall himself.
They all see Trini, but she climbs up a wall to avoid the kids. They chase after her, also climbing up the hill. Trini then makes a huge leap across a crevice. The others jump after her. Billy is the last to jump and almost doesn't make it. He pulls himself up the ledge and celebrates, only to fall down the crevice. The others think he's dead but then he starts laughing and telling the gang to join him. Jason and Zack jump in, but Trini starts to walk away.
Kimberly tricks her into coming back so she can pull her down with her. The kids all land in a body of water and swim down to find an underground cave. They come across a ship with advanced technology in it. A small robot named Alpha-5 (Bill Hader) finds the gang and brings them to Zordon, who now lives within the Morphing Grid to preserve his consciousness. Zordon and Alpha-5 explain to the gang that because the power coins came into their possession, they have been chosen to become the new Power Rangers. Zordon tells them about Rita and how she was originally part of their team until she betrayed her fellow Rangers for control of the Zeo Crystal.
She also wants to create Goldar, a gigantic golden monster that will tear apart Angel Grove to find the Crystal. The gang is then told to morph as they step onto the pads for the Morphing Grid, but they are unable to. Zordon decides they must start training. Despite his lack of confidence in the team, Jason tries to convince Zordon that he and his friends can prove themselves. Sam has a cop come onto his boat to check on the corpse they found. Rita's coin has revived her, and she attacks and kills the cop. The Rangers go back to the cave and must go into The Pit, where they are forced to fight against simulations of Rita's rock monster minions, the Putties.
The Rangers get beat up but they continue training and try to morph, but with no luck. They are then shown their Zords, which are huge mechas that the Rangers can control, but Alpha-5 and Zordon feel they aren't ready to use them. Zack disagrees and decides to take his Zord out. He is unable to control it and ends up running around outside the cave, nearly running into town before crashing back into the cave.
Jason gets angry with Zack and starts a fight. When Billy intervenes, the others see that he has morphed. However, he doesn't know how to get it started again. The Rangers set up a campfire outside the cave and decide to spend the night there. They decide to open up and get to know each other because they feel that's why they're not morphing. Zack starts and discusses his ailing mother while expressing his fears over what will happen to him if something happens to her. Billy relates as he had lost his father and lives with his mother. The reason he was in detention was because he blew up his lunch box.
Kimberly skips her turn, so Trini talks about how she's moved around a lot regarding personal issues. Jason acknowledges how people had seen him and how people may see him now as a result of his mistakes. Rita has been devouring gold off of several victims to gather for Goldar. She makes it into town and enters a jewelry store, where she starts consuming more gold and adding it to her staff. An officer arrives and orders Rita to stand down. She creates a Puttie and has it kill the officer.
Kimberly goes to Jason's house and admits to him why she was really in detention. The main reason was because she punched one of her friend's tooth out, but that was because he called Kimberly the meanest person ever. The reason for THAT was because one of Kimberly's friends sent her an explicit picture in confidence, only for Kimberly to spread that picture around. She felt guilty about it and thinks it's her fault that they aren't morphing. Rita attacks Trini in her bedroom. She taunts her with the fact that she killed the last Yellow Ranger. Trini and Rita fight for a bit, but Rita overpowers Trini.
She demands her to follow her orders. Trini is forced to lure her friends to the docks where Rita traps them all. She knows that Billy knows where the Crystal is. He discovered earlier that the Crystal lies beneath none other than... a Krispy Kreme. Rita heads off to find the Crystal but sends Billy underwater.
The others free themselves from their binds and try to pull Billy out. They try to revive him, but he is already dead. The four carry Billy's body to the cave. Jason expresses his sorrow and feelings that he failed Billy and his friends.
The Morphing Grid then activates, giving Zordon an opportunity to come back with his own body. After a brief moment, Zordon's face disappears from the wall. It then returns, and Alpha-5 asks Zordon why he didn't come back. He says only one may return.
Billy then wakes up, to the delight of his friends. Now that he sees they can work together as a team, Zordon tells the Rangers to step onto their pads. They finally morph into their suits and head off to stop Rita. The Putties attack the Rangers outside the cave as Rita is in the process of creating Goldar. The rock monsters outnumber the Rangers, so they hop in their Zords and beat them before heading into town. Goldar is already destroying Angel Grove to find the Crystal.
The Rangers head in and fight Goldar separately. Jason spots his father caught up in the chaos and he goes to rescue him, not revealing who he is. Goldar takes down Kimberly's jet and knocks the other Zords into each other. Goldar then starts to push the Rangers into a fiery pit as they start to accept their fates. Goldar knocks them all in, but they suddenly join their Zords together to create the Mega-Zord. Rita finds the Krispy Kreme and has Goldar tear it down to get the Crystal. However, the Rangers use the Mega-Zord to fight Goldar. Rita then lets Goldar absorb her so that she may give the creature more power.
The Rangers overpower Goldar and use their giant swords to destroy the monster. The gold melts off Rita and she faces the Rangers. Jason orders her to surrender so that they may take her to be judged by Zordon. Rita refuses and she leaps to attack the Rangers. The Mega-Zord simply smacks Rita into outer space where she is frozen. A crowd of citizens (including the original Green and Pink Rangers - Jason David Frank and Amy Jo Johnson) gather in awe of the Rangers.
The town recognizes the Rangers as their mysterious saviors. Sam hangs an article of their heroics on his fridge, implying he knows Jason is one of them. Zordon's voice is then heard as he expresses gratitude to the five friends for carrying on the legacy of the Power Rangers. Shortly after the initial credits, the teacher in detention is calling for Tommy Oliver, but he is not there. Moments later, Billy's locker blows up as a result of another one of his experiments..