Dr. Tommy Oliver, once the world's greatest Power Ranger has now retired as a science teacher at Reefside High after the destruction of his lab, and the disappearence of his partner Anton Mercer. As a mild manered science teacher, he finds himself stuck under the authority of the secretly villainous Principal Randall. When she puts him in charge of detention, he brings Conner: a hotshot soccer player, Ethan: a champion gamer, and Kira: a lone musician along on a fieldtrip to a museum. While the doctor's away, the bickering students fall into an underground lab, where they find the Dino Gems, which give them superhuman abilities. When Dr. Oliver learns that Mesogog, the one responsible for destroying his lab; has returned, he recruits the trio to become Power Rangers to fight against evil. With the power of the Dino Gems on their side, they must awaken robotic dinosaurs called Dinozords, which are a fusion of Dino DNA and technology.

When Mesogog uncovers another Dino Gem, Dr. Oliver must intervene and get a hold of it before it's able to be used for evil. As his students learn about his history as a Power Ranger, Tommy must reignite his past by bonding with new Dino Gem and lead the team as the Black Power Ranger. Tommy fights against the evil Zeltrax, when he discovers that Zeltrax has a score to settle with him. He was once a collegue of his, known as Terrance Smith, but after trying to compete with Tommy for a job, he was fatally wounded in a lab accident. Rebuilt as Zeltrax, he fights for revenge against Dr. Oliver.

Anton Mercer appears in Reefside after Tommy thought he had died in the explosion. Tommy is even more surprised to learn that Trent is his adopted son. But when Trent begins to question his fathers actions, he follows him through an invisiportal, where he finds himself in Mesogog's Island Fortress. After uncovering a Dino Gem tainted by evil, he is overtaken by its power, transforming into the evil White Ranger. Discovering that Anton is Mesogog, Trent joins the ranks of his evil army. But Anton reveals that Mesogog is a result of an experiment gone wrong; a side of himself that he can't control. As Anton fights the spell of Mesogog to save Trent, he accidently destroys the evil of the Dino Gem. As the White Ranger, he joins the other Power Rangers, hoping that his father can find a way to save himself as well.

As the Power Rangers begin to unlock the full potential of their Dino Gems, Tommy and Trent unveil the Shield of Triumph, a legendary power. With the combined power of the five Dino Gems, Conner steps up to accept his destiny by transforming into the Triassic Power Ranger.