The movie starts off with Piccolo meditating by the waterfall. Gohan drops by and shows Piccolo Haiya-Dragon's new trick: he dances to Gohan's whistling. Piccolo gets angry at Gohan when he shows the trick and yells at him. Suddenly Piccolo senses something out in space. Dr. Briefs (Bulma's father) sees what appears to be a planet out in space and it's heading straight for Earth! If it hits Earth will be destroyed! Klilyn vows to do something about it as a lazy Kamesennin(a.k.a. Master Roshi) sleeps. Gokou and Killilyn attempt to avert the oncoming planet's course with ki blasts, but they fail and are swept away. Miraculously the planet misses Earth and explodes far off. Everyone is saved, but the thought is short-lived as aliens arrive to conquer Earth. They come in the name of Lord Slug and proclaim him King of the Universe. Lord Slug, a very sickly and old looking alien, sits at his throne with his henchmen right beside him as his soldiers start to take innocent people's lives. Gohan stops the soldiers, though, and Slug takes notice of something on top of Gohan's hat: a Dragon Ball. He beats up Gohan, Bulma, and Oolong and takes the Dragon Balls, knowing what they can do, and it turns out that Slug is going to use Earth as his Cruiser just like the planet that exploded. He then gets the Dragon Balls gathered and wishes for his youth and power back. After that the aliens terraform(meaning they block out the Sun) Earth, covering it with thick clouds because all the aliens Except for Slug can't live in direct sunlight. Gokou and Killilyn are alive thanks to Yajirobe and his Senzu beans. Later in the night Gohan and Oolong run off to spy on the alien invaders. Gohan is spotted and almost caught, but is saved by Piccolo. They then face Slug's henchmen. Gohan fights Madamatcha, an imp looking alien. Madamatcha is too much for him though. Piccolo kills off his opponent easily and tries to help Gohan but is stopped by another henchman named Angila. Piccolo barely saves Gohan and they are both hurt very badly. Luckily they are saved by Gokou and Killilyn. Gokou easily kills Madamatcha and Angila, but then Lord Slug appears. Killilyn recklessly takes on Slug first and is beaten in one hit. Then Gokou and Slug fight, but Gokou can't even seem to hurt him. Gokou even tries to get energy from the Earth, but it doesn't have any since the Sun has been blocked. All seems lost until Gokou gets a sudden surge of energy and starts to beat on Slug. Then Slug decides to show Gokou his "true power," revealing that he is a Namek sei-jin: the same race as Piccolo! Slug then becomes gigantic in size. Kaiousama tells Gokou that Slug is not only a Namek. He is also a mutation and a Super Namek sei-jin. Slug starts to pummel Gokou again, but then Piccolo, who is also a Super Namek sei-jin, joins the battle. Piccolo rips off his own ears and tells Gohan to whistle. It seems that whistling is agonizing to Namek sei-jin just like high pitched sounds are to humans. That is why Piccolo yelled at Gohan when he started whistling to make Haiya-Dragon do his trick. The whistling was painful for him. Gohan starts to whistle and Slug then writhes in agony giving Piccolo the chance to give Gokou his power. Gokou then uses the infamous Kaiyouken technique to blast right through Slug's chest and finish him and his spaceship off. But Slug reappears and grabs a hold of Gokou. Gokou, however flies up high over the clouds so he can get energy from the Sun to form a Genki-Dama, killing off Slug once and for all. The clouds finally clear and Earth returns to normal. Kaiousama thinks Gokou might be the Super Saiyajin since he defeated Slug (although Gokou doesn't actually become Super Saiyajin in the movies until the next one). And Kamesennin finally wakes up from his nap!
