A probe-like machine flies to the Earth. Without thought, it starts a forest fire. Gohan and Krillin put out the fire and save a purple dragon. The forest is gone so they gather the Dragonballs and Gohan wishes the forest back. The next day the machine scans the planet and reports back to a group of pirates. They talk for a little while. We then discover that these space pirates are led by a Saiyan named Turles who wants to plant a tree that will give him fruit that can increase his power. The pireates decide that Earth is perfect for the Tree of Migh. They plant the tree and it drains the Earths energy, quickly destroying most of the land.

Gohan and Goku are at home relaxing. The purple dragon that Gohan saved follows him home. Chi-chi dislikes it, and tells gohan to get rid of it. Gohan keeps the dragon anyways. Yamucha buys a new flying car and wants to impress Bulma with it. While flying the car it's destroyed and Yamucha is left there.

Goku, Krillin, Yamucha, Tenshinhan, and Chaozu all head to the roots of the tree. Chi-chi makes Gohan stay home. They all try to blast the tree, but it's no good. The space pirates show up and start battling the Z fighters. Gohan sneeks out and finds the leader of the pirates who looks just like Goku. Turles talks to Gohan and finds out he's a Saiya-jin. He then creates a fake moon like Vegeta did and turns Gohan Oozaru. Gohan goes crazy and starts attacking Goku. Gohan sees the purple dragon he saved and it gets his attention. Turles then attacks Gohan so Goku cuts Gohan's tail off. The Z fighters are defeated so Turles' henchmen attack Goku, but he kills them all. Turles then attacks Goku and they seem pretty close in power.

Turles makes his way through the tree and eats a piece of the fruit, making him a lot stronger than Goku. Even using Kaio-ken x10 can't stop Turles. Knocked down to the floor and left to die, Goku gives it one last try, by making a spirit bomb to try to defeat Turles. Turles sees the ball coming at him and deflects it. Turles was able to deflect it since the Earth didn't have much power to give the bomb. Goku attempts another bomb, but this time he takes energy from the tree instead of the earth. He fires the bomb at Turles and finally hit hims. Turles is killed along with the Tree of Might and all the energy is given back to the earth. All is peaceful again on the Earth.