Goku, Krillin, Tien Shinhan and all the others go to dinner to celebrate their World Martial Arts Tournament victory (held during the Tien Shinhan Saga). Goku then realizes that he forgot his Dragon Ball and his Power Pole at the Stadium, so Krillin goes back to retrieve them. Sometime after he leaves, Goku senses that something is wrong and quickly rushes to find him. He finds Krillin's dead body and the World Tournament Announcer at his side.
The trembling referee explains that a hideous monster (later found to be Tambourine) killed Krillin and then flew off. He says that the monster also took a list of all the fighters in the tournament and Goku's Dragon Ball. Goku's friends soon follow him and also find Krillin's body. Enraged and grief-stricken, Goku grabs his Power Pole, takes the Dragon Radar from Bulma, and dashes off in pursuit of the killer despite Master Roshi's orders to stop, using the Dragon Radar in conjunction with his stolen Dragon Ball to track the killer down. Oolong finds a piece of paper with the killer's symbol on it nearby, and a horrified Roshi recognizes this symbol and Krillin's death as the work of the evil King Piccolo.
Master Roshi tells the others of a time when the world was suddenly over-run with hideous and seemingly invincible monsters, that made their way through civilizations, destroying all in their path. Eventually the creatures arrived at Mutaito's dojo, where in battle the entire school fought the monsters. However only a few of the monsters are killed while only two pupils made it through, Master Roshi and Master Shen. Master Roshi explains the monsters prepared a joint mouth blast and fired it at the two, but they concentrated their energy into a shield and fired the attack back, destroying them.
Following this, King Piccolo appeared before them and sends them flying into part of the Dojo with a single blast to the ground in front of them. Master Mutaito soon stepped in, but King Piccolo made short work of him, humiliating him in front of his students and leaving him for dead. After being nursed back to health, Mutaito left them both; while Shen eventually lost faith, Roshi did not. As King Piccolo's rampage continued, Master Roshi found refuge in the nearby mountains, where years later Mutaito returned to him, with an electric rice cooker.
Mutaito had trained hard and eventually used the suicidal Evil Containment Wave technique to trap King Piccolo in a jar. After personally disposing of the jar by throwing it into the ocean, Master Roshi founded the Turtle School based on Mutaito's teachings. Over time, civilization was rebuilt, and humanity forgot about King Piccolo's rampage.
However, Emperor Pilaf released King Piccolo after finding the jar and asking the Namekian villain to help him get the Dragon Balls, but King Piccolo had his own plans and instructed Tambourine to kill every fighter from the two previous tournaments, viewing them as potential threats.
Goku finally tracks down Tambourine and engages him in combat, but, as Goku is still weak from his fight with Tien, Tambourine easily outmatches him and destroys the Flying Nimbus, proceeding to beat Goku senseless and drop him to the ground, presuming him to be dead. Goku awakens battered and hungry in the middle of a forest, and soon stumbles upon a giant fish cooking over an open fire. Soon after he is confronted by Yajirobe, after which he is accused of eating Yajirobe's fish. They then have a quick fight in which they are evenly matched, with Goku surprised that Yajirobe is tough enough to take his punches and Yajirobe likewise surprised at how fast and strong Goku is. Meanwhile, Tambourine kills Bacterian, Nam, King Chappa, Pamput, Man-Wolf, Giran and other fighters.
King Piccolo then creates another son named Cymbal whose purpose is to find the Dragon Balls. Yajirobe has one, and this leads Cymbal to attack him. Yajirobe kills him, and, due to his hunger, eats him, saying he is excellent meat. Tambourine, who was getting ready to finish off Yamcha in a filler segment exclusive to the anime, is then ordered by King Piccolo to attack them in revenge for Cymbal's death, but at this point Goku is at full strength and kills him easily with his Kamehameha, completely incinerating him in the process. Yajirobe is then angry because he wanted to eat another creature that size.
Meanwhile, Master Roshi, Chiaotzu and Tien track down the Dragon Balls. King Piccolo reveals to Emperor Pilaf that he wants to use the Dragon Shenron to become young, and then proceed to conquer the Earth, "promising" Emperor Pilaf a fifth of his gain. Angry because of the death of his sons, King Piccolo goes to fight Goku himself, while Roshi and company find the Three-Star Dragon Ball in a cave, and head to where Goku and King Piccolo are fighting. Despite his age, King Piccolo has the upper hand, and soon Goku is defeated with ease. King Piccolo finds that Goku's heart has stopped and assumes him to be dead. He then takes the Dragon Ball from Goku's unmoving body and departs. However, after Piccolo leaves, Yajirobe (who had been hiding nearby) discovers that Goku's heart only stopped momentarily, and that the young warrior still lives.
Master Roshi lures King Piccolo with two Dragon Balls and confronts him, but is easily knocked around; knowing that he is no match for King Piccolo, Master Roshi merely stands still and takes King Piccolo's attacks. King Piccolo does not recognize Roshi until he mentions Mutaito; after which, he grows fearful, realizing what Roshi is here to do. After using a capsule to conjure an electric rice cooker, Master Roshi performs the Evil Containment Wave and nearly succeeds at trapping King Piccolo again, but misses the jar's opening at the last second. Before he dies from using the move, Master Roshi assures King Piccolo that he hasn't won yet and someone will succeed where he failed. With nobody left to stop him (Tien can't do anything because Master Roshi paralyzed him earlier with a knock-out potion, Chiaotzu is too weak, and Goku is too injured), King Piccolo summons the Shenron. Chiaotzu tries to stop him by wishing for his destruction, but is killed by King Piccolo's blast before he could finish his sentence. King Piccolo makes his wish to be young again, which results in his power rising to an incredible level.
King Piccolo became the Young King Piccolo, and as a sample of his newly replenished power, he kills Shenron, which causes the Dragon Balls to revert back to regular stones. The Dragon Balls no longer exist, and so none of the recently deceased people (namely Krillin, Master Roshi, and Chiaotzu) can be resurrected.
Goku asks Yajirobe to carry him to Korin Tower in order to get Senzu Beans. Luckily Yajirobe has his own car, in a capsule. Goku tries to climb, but because of his current condition, he asks Yajirobe to carry him, and they proceed up the tower. The now-rejuvenated King Piccolo is preoccupied with beginning his conquest of the world and begins by overthrowing King Furry and taking his title, supposedly making King Piccolo the king of Earth. but not before turning back on his promise to Emperor Pilaf and kicking him out of his airship.
Meanwhile, Tien went far away to train in use of the Evil Containment Wave Technique in order to trap King Piccolo. Goku finally reaches the top of the Korin Tower thanks to Yajirobe, and hears shocking news from Korin: Goku now is stronger than he and he therefore can't help him except by giving him Senzu Beans. However, he does mention the Ultra Divine Water, (not regular water, like the last time (see Commander Red Saga).
Yajirobe, and later Goku, enter a pot and travel on an icy road to a cave, fighting some monsters that resemble statues (but actually move and fight and aren't very nice). Also they find an illusions of Kame House and all of Goku's friends, that try to trick them, but Goku doesn't fall for the trickery. Finally, they meet the Guardian of the Ultra Divine Water: the Darkness herself and she allows Goku to drink the water: however, she tells Goku that if he doesn't possess some strength he will die by drinking it. Goku takes the chance, drinks it, and it works: after a night of suffering through pain caused by the water, he becomes stronger than King Piccolo.
King Piccolo is enjoying himself as he declares the new laws for the kingdom, including everyone should steal, no police activity, and no one can utter the words "peace" and "justice" or King Piccolo would become quite angry. He also creates a lottery to determine which province will be attacked next: the first province will be where Bulma's parents are living, but as luck would have it, Tien has just mastered the Evil Containment Wave and is on his way to battle Young King Piccolo and Goku (who was given a new Flying Nimbus by Korin) flies as fast as he can to challenge Piccolo to a rematch.
Tien reaches the palace first, and battles another child of King Piccolo: Drum. Drum is as strong as he is fat, and defeats Tien easily. Desperate, Tien performs the Evil Containment Wave on King Piccolo, but Drum jumps in the way and is caught. Before he can be sealed, King Piccolo destroys the electric rice cooker, sparing Tien's life and saving Drum from imprisonment (this is only in the anime; in the manga, Tien immediately attempts to perform the Evil Containment Wave on King Piccolo, but notices that the rice cooker he had intended to use is cracked, meaning King Piccolo could escape once trapped and with no other options, Tien challenges King Piccolo and fights Drum). At that moment, Goku arrives, and Tien is relieved to see that Goku is still alive. Goku notices that King Piccolo has regained his youth and full power, which King Piccolo confirms before ordering Drum to attack Goku. Tien warns Goku to run, but Goku simply kicks Drum in the face so hard that his eyeballs pop out, killing him.
Tien stares in awe, shocked at how Goku has become so strong since the last time he saw him, as he killed Drum with one kick. King Piccolo tells Goku he doesn't have time for him again because he is on his way to West City, and that he will have to make his demonstration quick.
Tien is even more amazed at how Goku has blocked all of Piccolo's attacks. Goku tells King Piccolo that he is going to make him pay. At that moment Goku seemingly disappears then reappears in front of King Piccolo, sending a powerful punch to his face. The powerful punch sends King Piccolo flying in Piano's direction, crushing Piano with the fall. An enraged King Piccolo gets up and rushes at Goku, at first Goku is able to avoid King Piccolo's attacks, but then King Piccolo manages to hit Goku. Goku recovers remarkably quickly and charges back with a powerful barrage of punches and kicks, seemingly finishing the Demon King. King Piccolo is unhurt, however, and tells Goku that despite the fact that it will shorten his lifespan, he will power up to his full strength.
King Piccolo begins powering up, the ground begins shaking and breaking apart, and Tien begins to have a hard time keeping his balance, but Goku stands unaffected. Piano's body is sunk into the rubble and soon King Piccolo begins seemingly glowing. King Piccolo then finishes powering up and attacks Goku, sending a powerful punch to his body that sends him to the ground so hard that it creates a large impact crater. Both King Piccolo and Tien think Goku is dead, and Tien prepares to fight, but then they hear a voice ring out: "Ka...me...ha...me...HA!!" Goku is alive, and he shoots a Kamehameha at King Piccolo. King Piccolo notices and prepares to block it, but Goku was now able to use a homing version of the Kamehameha and Young King Piccolo was hit by the homing blast. Subsequently, Goku and King Piccolo continue combat.
Meanwhile, a stunned King Furry was watching the fight, and wanted to stay and watch King Piccolo be defeated, but one of his guards convinces him they must reach higher ground while they still have the chance. King Piccolo is knocked into another building, he gets up and throws a piece of it at Goku, and Goku blocks it, King Piccolo then used his eye-laser to burn Goku's knee, but Goku replies he only needs one knee to finish him. King Piccolo laughs, and then prepares another chop attack, but Goku gets his Power Pole and orders it to extend, sending him flying towards Piccolo, Goku then uses his good knee to knee King Piccolo in the face.
On the television, people say there is a huge battle in the ruins of the King's Castle between King Piccolo and "a very bald young man, and a small boy". Bulma wonders if Goku is alive, but Yamcha assumes he is dead Bulma then points out how Fortuneteller Baba once told them Goku would someday become a great hero. The two are convinced it is Goku and that he will save the world from Piccolo.
King Piccolo is enraged at Goku's attack and states the Power Pole is only a crutch. King Piccolo then proceeds to increase his size, making himself even more massive than before, and neither Goku or Tien know what is happening. King Piccolo starts firing large powerful finger blasts which Goku blocks with energy attacks of his own. He eventually fires at Goku's Power Pole, removing it from the fight, then fires his Explosive Demon Wave which creates an explosion of near-nuclear effect. The TV loses signal while King Furry and his two guards narrowly escape King Piccolo's blast.
King Piccolo is shocked to find that Goku survived the attack; Tien had flown him up into the air to escape the blast. Goku says he can manage without Tien (who is now completely drained of all his energy). King Piccolo powers-up again for a slightly weaker Explosive Wave, and Goku tries to stop him with a punch, but the punch isn't strong enough to knock Piccolo out because Goku was unable to build up enough momentum with only one leg. King Piccolo completes the blast, hitting Goku and sending Tien flying several feet away.
King Piccolo, now exhausted, believes he has destroyed Goku when then he hears his voice from within the massive crater. The Flying Nimbus brings Goku back up and he prepares to attack again, King Piccolo appears too exhausted to continue, but he quickly runs out of range and picks up Tien by his head and begins squeezing it, demanding if Goku does not surrender to him he will crush Tien's skull. Tien pleas with Goku to forget about him and make sure he destroys King Piccolo, while King Piccolo tightened his grip on Tien's head.
Meanwhile Yamcha, Bulma, and Launch land and explore the ruins of the city to make their way to the source of the blast. Elsewhere Yajirobe has decided to come see Goku fight, but then begins to have second thoughts seeing the giant crater. Yajirobe then begins to debate with himself whether or not to go back after remembering Goku promised him a free dinner for taking him to the Tower.
Goku finally says he will do whatever King Piccolo wants. King Piccolo tells him not to move, and picks up a rock, and with his powerful breath propels it at Goku, hitting his arm and breaking it. Goku holds his arm in pain and tells Tien to forgive him but he can't let King Piccolo get away with what he's done. King Piccolo asks him if he cares for Tien's life and Goku says he will just have to revive him with the Dragon Balls. Hearing this, King Piccolo laughs at him and says he's already killed Shenron, shocking and angering Goku. With no other way to save Tien, Goku stands still, and King Piccolo picks up another rock and propels it at Goku's good knee, breaking it.
Satisfied Goku is helpless, King Piccolo drops Tien and states he will finish him later and kill Goku now. King Piccolo rises high up into the sky again and begins charging at Goku at top speed. With his right arm unharmed, Goku blasts a large one handed Kamehameha that propels him back at King Piccolo at supersonic speed.
Goku prepares to put all of his strength into one single punch, but King Piccolo prepares to block it. Goku shouts "It's time for your terror to end!" and launches the punch, suddenly the image of the Great Ape appears with Goku as he flies towards King Piccolo. A loud explosion rings out and Tien looks up; Goku has punched a hole clean through King Piccolo's chest. As Goku sobs with victory, King Piccolo can only hover, dying, shocked he has been killed by someone, but states Goku's only won for now. King Piccolo then spits out his last egg which contains Piccolo Jr., an offspring designed to carry all of his father's strength all the way from birth. King Piccolo swears vengeance upon Goku and explodes. The shockwave of the explosion sends Goku flying fast to the ground below, but just before he lands Yajirobe shows up and catches him. Before they part ways, Tien says he's going back to the Kame House to tell the others, while Yajirobe prepares to drive Goku back to Korin Tower.