In the movie, the Z-Fighters face a new threat that starts with the burning of a forest, in which Gohan and Krillin rescue the forest animals and a small dragon named Icarus. Although they are able to restore the forest to its normal state with the Dragon Balls, Icarus doesn’t return and stays with Gohan, much to Chi-Chi’s fury. Goku then shows a nearby cave to let Gohan keep the dragon with him. Later, the Earth is visited by an unfriendly group of aliens under the leadership of a Saiyan. Upon arriving, they plant a seed which grows the Tree of Might, a plant that sucks the life of the planet on which it was planted and leaves it a desert. At King Kai’s request, Goku, Krillin, Yamcha, Tien and Chiaotzu investigate and try to destroy the Tree, but are unsuccessful. They are then confronted by the aliens whilst their leader watches from inside the spaceship. Eventually, Krillin, Yamcha, Tien and Chiaotzu are defeated by the aliens, with only Goku remaining as the one who can hold his own against them.
During the ensuing battle, Chiaotzu is rescued by Gohan, who had just arrived, and demonstrates his incredible fighting skills by easily taking out the two identical aliens. He is then encountered by the aliens’ leader Turles, a Saiyan who bears a striking resemblance to Goku. Turles gives Gohan a choice to either join him or die. Gohan refuses to join Turles, and is saved in time thanks to the arrival of Piccolo. However, Turles defeats the both of them and creates an artificial moon, turning Gohan into a Great Ape and sets him on Goku, who is almost crushed to death in Gohan’s hand until Icarus arrives and calms Gohan down. But when Turles attacks Icarus, Gohan is angered and turns on Turles, who fires an attack at Gohan. Before the attack can make contact, Goku manages to cut his son’s tail off and restore him to normal. Cradling the little one in his arms, Goku threatens Turles. Angry and impressed at the same time, Turles sets his henchmen on Goku, who uses the Kaioken attack and makes quick work of them while Piccolo unsuccessfully fights Turles again. Goku and Turles then fight, with Goku having the upper hand, until Turles pushes his power further by eating a fruit from the Tree of Might. With his new power, Turles dominates Goku and beats him to the point that he is no longer able to fight, even with the use of the Kaioken x10 (x20 in the funimation dub).
Slowly recovering while Turles is distracted by the rest of the Z-Fighters, whom he brutally dispatches, Goku decides to use his Spirit Bomb. Despite gaining energy from the living, he is not able to attack Turles as he counterattacks with a blast of his own, neutralizing Goku’s Spirit Bomb. Unable to gather more energy from living beings, Goku decides to steal energy from inside the Tree of Might itself. Eventually successful in creating the Spirit Bomb, Goku sees his opportunity, and fires it straight into Turles, who is carried up the trunk of the Tree of Might and destroyed along with the Tree when the Spirit Bomb explodes. With the terror now over, the Z-Fighters return to their normal lives once again.