The beginning of the Dragonball Z saga...
Gokou has grown up since the Dragonball series and married Chi-chi and they've had a son named Gohan. Gokou and Gohan go to Master Roshi's for a reunion with Krillin and Bulma. While there, Gokou's brother Raditz arrives and Gokou learns that he is a Saiyan and meant to destroy the earth. After Gokou refuses to help Raditz, Raditz kidnaps Gohan and tells Gokou to start killing. Piccolo, who met Raditz earlier, shows up and proposes an alliance to fight Raditz. Gokou and Piccolo leave to fight.

Piccolo and Gokou fight Raditz for awhile, until Gohan stuns Raditz with incredible power and Gokou grabs him. Piccolo hits Raditz (and Gokou) with his most powerful blast. They both lie dying. Piccolo tells Raditz that Gokou will be wished back to life, and Raditz transmits the knowledge of the dragonballs to Vegeta and Nappa.

Bulma, Roshi, and Krillin arrive on the scene, and Piccolo tells them that he is going to train Gohan. Meanwhile, at Kami's request, Gokou is allowed to set out for King Kaiou's in the otherworld. To get there he has to run 10,000 miles along Snake Way. Krillin, Yamcha, Tenshin-han, and Chauzu all go to train with Kami back on earth.

Piccolo brings Gohan to a desert to survive, and removes his tail. Yamcha has to quit baseball to train with Kami. Chi-chi, and to a lesser extent Ox King, become furious with worry until master Roshi tells them what happened. Bulma and Krillin decide to get the dragonballs so they can wish Gokou to life. Gokou falls off Snake Way, but manages to recover. A year passes...

About one year later Vegeta and Nappa arrive on earth. The first battle that takes place is against the Saiba-men, during which Yamcha dies. Next the earth warriors fight Nappa while Vegeta watches. Tenshin-han, Piccolo, and Chauzu all die. Then Gokou arrives and defeats Nappa. Vegeta is dissapointed so he kills Nappa. Gokou begins to fight Vegeta, and Vegeta creates a moon so he can be an ape monster. Yajirobe cuts off Vegeta's tail, but then Gohan's tail grows back and he turns into an ape monster. Gohan beats Vegeta within an inch of his life before Vegeta cuts off Gohan's tail. Gokou spares Vegeta's life and Vegeta leaves.