The movie begins with Piccolo being attacked and supposedly killed by a group of shadowed fighters. The movie then cuts to Chi-Chi along with her father, Ox King, and Gohan being attacked by an unknown group of fighters. Goku is out fishing during the attack and after sensing danger, he returns only to find his son has been kidnapped. The group responsible for the attack are Garlic Jr.'s henchmen, and it is later revealed that they were not so much holding Gohan ransom for any reason, but because they were after the four-star Dragon Ball that was attached to his hat. After retrieving the remaining Dragon Balls, Garlic Jr. summons Shenron and he immediately wishes for immortality. Shenron never having to grant this type of demand before, grants Garlic Jr. his wish. A furious Goku arrives to try and take back his son, but soon discovers Garlic Jr.'s new power. Kami meets up with Goku, and describes a brief history of Garlic Jr. and his father Garlic. Goku then proceeds to try to find Gohan when he is attacked by the villain's gang.
After brief fighting, Krillin and Piccolo appear and together they defeat Garlic Jr.'s henchmen Ginger, Nicky, and Sansho. And with Garlic Jr.'s newly obtained immortality and a new muscular second form, it seems not even Earth's warriors can take him down. Confident Garlic Jr. unleashes his ultimate attack, and bursting with anger, he opens up a portal known as the "Dead Zone" (hence the name of the film). Intending to suck his enemies into the void, Garlic Jr. becomes frustrated with Goku's ability to avoid the Dead Zone, and he decides to handle Goku himself, and later force him into the Dead Zone. Things looking extremely difficult for Earth's hero, Goku's son, Gohan, becomes enraged witnessing his father and friends in danger and releases his latent energy, blasting Garlic Jr. into his own vortex to be trapped for an eternity. Remarkably, in the end of it all, Gohan doesn't remember a thing of what happened, and with amazement, Goku figures his son is no ordinary boy, but one with a great hidden potential.