Seven years have passed since the end of the Dragonball series, and Goku has settled down after he and Chi-Chi have their first child, Gohan. All is peaceful until Goku's evil brother, Raditz, lands on the Earth. He tells Goku that he belongs to an alien race known as the Saiyans, 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. Raditz offered Goku to join him in conquering the universe, but of course he was turned down. Angered that he would not do his bidding, Raditz 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 Raditz. Piccolo tells Goku of a new attack he has been working on, one that should be able to defeat Raditz. However, it takes a long time to charge up, so Goku has to face Raditz alone for five minutes. Goku puts up a good fight, but gets socked around quite a bit. Piccolo fires his Special Beam Cannon(Makankosappo) while Raditz is busy with Goku, but he misses. Gohan, enraged by the pain being done to his father, attacks Raditz and greatly weakens him. Goku manages to get Raditz in a hold, and tells Piccolo to charge his attack again. Piccolo fires his Special Beam Cannon(Makankosappo) a second time, hitting both Raditz and Goku. They both die in a matter of minutes.
Before dying, Raditz is told about the Dragonballs and their power to grant any wish. He signals the other two Saiyans, Nappa and Vegeta, 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 King Kai of the North in hopes of growing more powerful for the coming evil. King Kais planet exists at the end of a ten-thousand mile long "snake road".
Months have passed on Snake Way, and Goku has yet to find King Kais hous. 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 King Yamma 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 atraining routine that leaves Gohan beaten to a pulp. Slowly but surely, Gohan's power is tapped into.
Krillin, Yamcha, Tienshinhan, Chaozu, and Yajirobe head off to Kami Look-Out on the top of Korin Tower to train for the arrival of the Saiyans. Their various methods prove to be effective, and they manage to each raise their power levels to over a thousand.
When Goku finally reaches King Kais, he undertakes a series of training exercises that seem trivial and pointless to Goku. His first task is to catch King Kais 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. Gokus's second task involves hitting Gregory, a flying cricket, 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 King Kai finally teaches our hero some techniques: The Spirit Bomb and The Kaio-ken power-up. With only a few days before the Saiyans 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.
A year has passed, and the Saiyans land in a heavily populated city. After destroying it, they head to battle Piccolo and the others. Assessing their opponents, Vegeta notices that one of the warriors, Piccolo, is an alien known as a Namek. The Saiyans unleash six Saibamen, each roughly as powerful as Raditz was (about 1,200). Vegeta suggests that the Earthlings fight the Saibamen one on one, and they agree. Tienshinhan 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, Vegeta has all the Saibamen attack at once. The small green aliens prove to be no match for the Z warriors. With their minions gone, Nappa joins into the fight. Our heros are unable to land many hits, and take a lot of damage. Both Tienshinhan and Chaozu sacrifice their lives trying to defeat the muscular Saiyans, but neither succeed.
Krillin tells Vegeta 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 Goku gets back to Earth. Seeing that Goku might be a problem, Vegeta 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. Krillin 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. Vegeta's bodyguard is unable to land any blows, and the Saiyan prince takes Nappa out himself.
Goku and Vegeta square off, beginning their long duel. While Goku manages to hurt Vegeta badly, his repeated use of the Kaio-ken technique puts a great strain on his body. Seeing that he was overpowered, Vegeta transforms himself into an Oozaru. Goku is chased around by the giant ape, and with the use of the Solar Flare for distraction, he is able to gather a Genki-dama. Unfortunately, Vegeta 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, Vegeta's tail is severed by Yajirobe's sword.

Back in his original form, Vegeta begins to do battle with Gohan. Meanwhile, Goku summons Krillin and gives him the remaining Energy of the Spirit Bomb he had gathered. Just when it looks as if Gohan will be defeated, Krillin launches the bomb at Vegeta. He evades it, but Gohan bounces the attack and hits Vegeta from the rear.
Thinking Vegeta is dead, our heros begin to celebrate. However, they notice Vegeta's body slowly falling to the ground. He is still alive. Vegeta and Gohan resume their battle, and it looks like the Saiyan prince will claim victory. However, Yajirobe intervenes again, and slashes Vegita in the back with his sword. When he gets over the shock of being slashed from behind, Vegeta kicks the crap out of our fat samurai friend. This gives Gohan ample time to stare up at the false moon Vegeta had created and transforms into an Oozaru.
With little energy to defend himself, Vegeta is smacked around by Gohan. Having exhausted himself, Vegeta uses a Kienzan to remove Gohan's tail. What he doesn't account for is having enough strength to get out of the way of the monkey's massive body. He is painfully crushed by the ape, who returns to being normal Gohan after a few moments. Vegeta summons his space pod, and tries to crawl to it. Krillin refuses to let him escape, and puts Yajirobe's sword up to Vegeta's throat. Goku begs him to spare the Saiyan's life, and reluctantly Krillin complies. Vowing to return, Vegeta flies away...