The film opens with Son Gokū's death and the death of the Z-Fighters at the hands of Jinzō'ningen (Artificial Human) #17 and #18 (Cyborgs #17 & #18) (Note: They cannot come back because the Dragon Balls are permanently unusable due to Piccolo's death.) The TV Special moves into the future where Trunks is a 13-year old teenager and 23-year old adult Son Gohan is the only one able to stand against the Jinzō'ningen, due to the fact that all the Z-fighters death resulted in him becoming a Super Saiyan. Gohan trains Trunks in fighting and power. Trunks tries to become a Super Saiyan, but cannot, although he keeps coming very close. One day, The Jinzō'ningen attack an Amusement Park. Gohan and Trunks come to the aid of the people. Jinzō'ningen #17 takes on Gohan while Jinzō'ningen #18 sits back. Gohan transforms into a Super Saiyan and, despite a few lucky hits by #17, quickly takes control of the fight.
However, #18 joins the fight and begins to beat Gohan, but Trunks, although no match for the Jinzō'ningen comes to the rescue and takes on #18. He manages to fight her for a minute before he is beaten, but Gohan saves him from death. Gohan and Trunks hide in the debris, while #17 and #18 figure they left, but blow the park anyway. Gohan and Trunks survive the blast, but at the cost of Gohan's left arm. Gohan recovers, and resumes training Trunks. The training is stopped short when the Jinzō'ningen attack the Capitol (only called "The Capitol" in the Japanese version). Trunks wants to fight, but Gohan knocks him unconscious. Gohan, with only one arm, ambushes #17 and damages his clothes. Gohan, despite his handicap, puts up a long suspenseful fight against the Jinzō'ningen, but meets his end when the Jinzō'ningen knock him to the ground and shoot ki-blasts (ki=energy) like a machine gun from the sky, which kills Gohan. Trunks is awakened by the vanishing of Gohan's ki. Upon searching the city, Trunks finds Gohan's dead body. The rage from within him is unleashed and Trunks transforms into a Super Saiyan. The story moves forward 3 years later. Trunks is now 16 years old. While Bulma is working on the Time Machine, Trunks goes off to fight the Jinzō'ningen. Trunks barely puts up a fight and is eventually beaten by the merely toying Jinzō'ningen. Jinzō'ningen #18 tries to kill him with a large blast of ki, but Trunks miraculously survives. He awakes in his house, with Bulma by his side. After a brief talk, he decides to go in the Time Machine (once it's finally ready, which is about 6 months to a single year later) and give the heart medicine to Gokū.
Later, however, after returning from his trip to the future, Trunks happens to come across the Jinzō'ningen again as the Jinzō'ningen expect another vapid fight. Trunks does better, but still needs to improve, and decides to return to the past, 6 months to 1 year later, to see how the battle with the Jinzō'ningen turned out.