The Saiya-jin Saga all starts off when Goku goes to Mr. Roshis island for a visit, since he hadnt seen his friends in years. They were planning on having sort of a reunion. The only ones who are there is Krillin, Bulma, and Master Roshi. Goku comes in and brings along a little guy that looks a bit like Goku when he was smaller. Goku tells them that it is his and Chi-chi's son. His name is Gohan, just as he is being presented to Goku's friends a human like alien by the name of Raditz appears.
He tells them all that he is Gokus older brother, and that he comes from another planet called Planet Vegeta. He tells them all that he had come back to check up on his brother. Everyone is suprised and Goku tells him that he doesnt remember anything. This is when we find out that Goku fell on a mountain side when he was small, and suffered from amnesia. He had forgotten his mission of destroying all of the inhabitants of Earth. Raditz asks Goku what happened to his tail, and Goku tells him that it had been cut off for good. Radditz gets enraged and tells Goku that it (the tail) is their true power. Raditz explains that they come from a race of warriors, a race by the name of Saiya-jin, and when they see the full moon they can turn into a waremonkey called Oozaru. This is when Goku first finds out that it was he, Goku, that had killed his grandfather many years ago.
Goku gets angry and attacks Radditz, but Radditz shows to be a lot stronger than Goku and knocks him out in one hit. Radditz notices that Gohan has a tail and so learns that it is Gokus son. He takes him hostage and leaves. Just as he leaves Piccolo comes in! Everyone is surprised at the arrival of Piccolo. Piccolo explains that Goku will not be able to defeat Raditz, not alone. This is when an alliance forms between Goku and Piccolo. They agree to work together to finish Radditz off. Piccolo explains that he is not doing this to rescue Gohan, but because Radditz is coming between Piccolo's plans of conquering the world.
Goku and Piccolo have no trouble finding them since Gohan had a dragonball on his hat. They followed them with the Dragon Radar (remember it form Dragonball). They arrive to find Gohan trapped crying in Radditz space ship. They must first fight Radditz to get Gohan so they do this. At first it looks really bad for Goku. Gohan is still trapped in the space ship and with a rage of anger his power level increases tremendously. He manages to break the spaceship and goes directly for Radditz and head butts him, which causes Radditz's armor to break, but Radditz then pushes Gohan away. Everyone is surprised at Gohan's high power level. Piccolo and Goku are still fighting and then Goku is able to get hold of Piccolo and tells him to do his finishing attack, which goes through Radditz and Goku as well.
Radditz asks why Goku sacrified his life just to destroy him, Piccolo explains to him that he can easily be revived by the Dragon Balls. Radditz explains to Piccolo that everything that he just told him was also told to Radditzs fellow Sayans, the last of the Saiyans, and that they were going to come to Earth to finish them off and find the Dragonballs within a couple of months and that they are a lot stronger than he, then dies. Goku dies as well.
So now everyone has to start training for the arrival of the other Sayans, which are supposed to be way stronger than Raditz. Picollo kidnaps Gohan and decides to train him. He lets him alone in a deserted island to live on his own for a couple of months, and if he lived, he would then be worthy of receiving training. The months go by and Picollo then trains Gohan, while Krillin, Tenshinham, Yamcha, Yajirobe, and Chaozu receive special training by Kami-sama. At the same time this is happening, Goku is still in heaven and training as well. He goes out and trains with the great Kaio-sama, there he learns how to do the Kaioken and the Genki Dama (Spirit Bomb).
The Saiya-jin's arrive just as told and Yamcha is the first to die. He gets killed when Nappa plants five Saibiamen, which are little green men, and one of these easily kills him. After Yamcha dies, the little green men are all killed. Goku had been revived, but not at the battle field yet. The two Saiya-jin's names are Nappa and Vegeta. Vegeta does not fight at all, but just watches and gives orders to Nappa. This is when Piccolo first finds out about who he really is since the Saiya-jina call him a "Namek-jin". The next to go is Chaozu when he self-destucted in an attempt to kill Nappa. But this did nothing to Nappa. Tien is enraged and goes for Nappa, but gets a limb cut off and later dies. Then Piccolo and Krillin come in and attack him in mid air when he is not seeing. As Nappa is heading to hit the Earth, Piccolo and Krillin both scream at Gohan to finish him off, but Gohan show his cowardness and does nothing. This might of been their only chance to defeat him. Vegeta tells Nappa to stop messing around, but to wait a while longer for Goku for the fight to really start.
After Goku is revived, he first goes to Karin tower to pick up some Senzu beans and takes off in his Flying Nimbus. Gohan gets extremely angry after Nappa knocks Piccolo unconcious in an attempt to grab his tail, which is supposed to be a Saiyan's weak spot, but Nappa had over come that already. Gohan attacks Nappa, but does no real damage. Then Krillin attacks too, and too has no real damage. Nappa gets angry and sends a powerful attack towards Gohan, but is blocked by Piccolo, and so Piccolo dies.
Goku finally arrives with a power level of 5,500 and increasing. He comes to find out that all of the Z warriors, except for Krillin and Gohan had died and attacks Nappa. Nappa is astonished at Goku's power. Vegeta then says that he will personally kill Goku and so Nappa goes towards Krillin and Gohan. Goku does the Kaioken which leaves Nappa on the floor. Nappa asks Vegeta for help, but Vegeta kills him in cold blood for being weak. The fight between Goku and Vegeta begins, Vegeta is then astonished at Goku's power. Since this proves to be a hard match for Vegeta, he decides to turn into Oozaru. Goku decides to do the Spirit bomb, but he needs time to do this. So he does the "Solar flare" to blind Vegeta for a little while. But Vegeta is too quick and tortures Goku up to the point where he is almost dead. Yajirobe, which had been in hiding all along comes out of no where and cuts off Vegeta's tail, so now Vegeta goes back to his normal size. Gohan steps into the fight now although he knows he is no match for Vegeta. Goku, now badly hurt, calls Krillin and tells him to do the Spirit Bomb for him (Goku had still been collecting energy during this time). Krillin gets the energy and waits for just the right moment to use it. Krillin fires it, but misses, Gohan gets it back and throws it again and this time hits Vegeta. This sends Vegeta through the air, but is not defeated yet. Since Vegeta had made an artificial moon to turn into Oozaru, Gohan happens to look at it and then too transforms into Oozaru. Now the tables have turned. Gohan, as Oozaru, lands on Vegeta and is now defeated. Krillin, now really weak, finds his last strength to finish Vegeta off by killing him with Yajirobe's sword, but Goku decides not to kill Vegeta and lets him go.