|Seven years have passed since the end of the Dragonball series, and Goku has settled down after he and Chichi have their first child, Gohan. All is peaceful until Goku's evil brother, Raditsu, lands on the Earth. He tells Goku that he belongs to an alien race known as the Saiya-jin, and that he was supposed to exterminate all life on the planet so that it could be sold to the highest bidder. However, since Goku hit his head as a kid, he forgot his orders and became a peace-loving child. Raditsu offered Goku to join him in conquering the universe, but of course he was turned down. Angered that he would not do his bidding, Raditsu kidnaps Gohan.
Obviously overpowered, Goku teams up with his arch-rival Piccolo to get his son back. Both attacking at the same time, Goku and Piccolo are still no match for the battle-hardened Raditsu. Piccolo tells Goku of a new attack he has been working on, one that should be able to defeat Raditsu. However, it takes a long time to charge up, so Goku has to face Raditsu alone for five minutes. Goku puts up a good fight, but gets socked around quite a bit. Piccolo fires his Makankosappo while Raditsu is busy with Goku, but he misses. Gohan, enraged by the pain being done to his father, attacks Raditsu and greatly weakens him. Goku manages to get Raditsu in a hold, and tells Piccolo to charge his attack again. Piccolo fires the Makankosappo a second time, hitting both Raditsu and Goku. They both die in a matter of minutes.
Before dying, Raditsu is told about the Dragon balls and their power to grant any wish. He signals the other two Saiya-jins, Nappa and Vegita, to come to Earth so that they may take the dragonballs for themselves. The journey to Earth takes one year, giving the Earthlings little time to prepare. Meanwhile in heaven, Goku begins his voyage to the Kaio of the North in hopes of growing more powerful for the coming evil. Kaio-sama's planetoid exists at the end of a ten-thousand mile long snake path.
Months have passed on the Snake Way, and Goku has yet to find Kaio-sama's home. Offered a ride by a passing demon, Goku falls fast asleep. Unfortunately, a bump in the path sends Goku flying off the machine and into Hell. When Goku wakes up, he is confused to find two demons looking over him. They tell him that he has fallen off Snake Way, and that the only way out was to beat them in a contest. Goku easily wins both times, and is shown the exit to Hell. He is surprised to find that the exit is merely Enma-sama's droor, and that he has to start his journey all over again.
Meanwhile, Piccolo begins to teach Gohan how to survive on his own in the wilderness while still training on his own. He gives Goku's son little help in his battle against dinosaurs and the elements. Yet Gohan is not to be under-estimated, and he does quite well on his own. When Piccolo feels he is ready, he begins a rigorous training routine that leaves Gohan beaten to a pulp. Slowly but surely, Gohan's power is tapped into.
Kuririn, Yamcha, Tenshinhan, Chaozu, and Yajirobe head off to Kami-sama's tower to train for the arrival of the Saiya-jins. Their various methods prove to be effective, and they manage to each raise their power levels over a thousand.
When Goku finally reaches Kaio-sama, he undertakes a series of training exercises that seem trivial and pointless to Goku (Not only that, but he has to withstand Kaio's lame humor). His first task is to catch Kaio's pet monkey Bubbles, who is used to the high gravity of the planet. Goku finds that it's quite a chore to chase after something in 10x gravity, but eventually he grows used to the heavy force. Through the use of some clever tricks, Goku captures the monkey. Son's second task involves hitting Gregory, a flying cricket creature, with a heavy mallet. Nearly destroying the planetoid in the process, Goku manages to complete the second part of his training with ease. It's at this time that Kaio finally teaches our hero some techniques: The Genki-dama and Kaio-ken power-up. With only a few days before the Saiya-jins are supposed to arrive, Goku has to make the trip along Snake Way in the opposite direction. Luckily, his training had improved his speed and power exponentially.
A year has passed, and the Saiya-jins land in a heavily populated city. After destroying it, they head to battle Piccolo and the others. Assessing their opponents, Vegita notices that one of the warriors, Piccolo, is an alien known as a Namek. The Saiya-jins unleash six Saibamen, each roughly as powerful as Raditsu was. Vegita suggests that the Earthlings fight the Saibamen one on one, and they agree. Tenshinhan is the first to go, and makes short work of the first Saibaman. Yamcha goes next, and appears to be winning until his opponent grabs hold of him and self-destructs (Killing both). Growing bored with the situation, Vegita has all the Saibamen attack at once. The small green aliens prove to be no match for the seasoned Z warriors. With their minions gone, Nappa joins into the fray. Our heros are unable to land many hits, and take a lot of damage. Both Tenshinhan and Chaozu sacrifice their lives trying to defeat the muscular Saiya-jin, but neither succeed.
Kuririn tells Vegita to wait for Goku to arrive, as then they would have a fighting chance. They wait for three hours, but no Goku. The battle resumes, when finally Son gets back to Earth. Seeing that Goku might be a problem, Vegita orders Nappa to kill the others before Goku arrives. The large brute decides to go after Gohan first, and charges a powerful attack. However, Piccolo had grown to love Gohan over the year he had spent training him, and the Namek put himself in the way of Nappa's attack. Kuririn and Gohan are the only survivors when Goku finally joins the battle. Angered by the death of his friends, Goku maintains his cool and stay calm battling Nappa. Vegita's bodyguard is unable to land any blows, and the Saiya-jin prince takes Nappa out himself.
Goku and Vegita square off, beginning their long duel. While Goku manages to hurt Vegita badly, his repeated use of the Kaio-ken technique puts a great strain on his body. Seeing that he was overpowered, Vegita transforms himself into an Oozaru. Goku is chased around by the giant ape, and with the use of a Taiyoken for distraction, he is able to gather a Genki-dama. Unfortunately, Vegita recovers before the attack can be launched, and most of the energy is lost. He grabs onto Goku and breaks every bone in his body, but neglects to notice Yajirobe sneaking up behind him. With one swipe, Vegita's tail is severed by Yajirobe's sword.
Back in his original form, Vegita begins to do battle with Gohan. Meanwhile, Goku summons Kuririn and gives him the remnants of the Genki-dama he had gathered. Just when it looks as if Gohan will be defeated, Kuririn launches the ball at Vegita. He evades it, but Gohan bounces the attack and hits Vegita from the rear.