After Vegeta has returned from his search for Goku, he and his new allies, the Z warriors, notice a mysterious youth in the distance fighting 2 strange enemies. It is Trunks! Vegeta's son from the future. He comes back with medicine for Goku's heart condition, that Goku doesn't even know he has. Frieza was rebuilt by his father King Cold, and the duo comes to Earth to exact revenge. Trunks makes quick work of the two of them and delivers a warning to the Z warriors that in 3 years the Earth will fall to a group of malicious androids. Trunks leaves to return to his own time, promising to return in 3 years.
After Trunks came to the past at the end of the Frieza Saga and warned the Z Warriors about the coming Androids, everyone trained for 3 years in anticipation of the day the Androids would arrive to destroy mankind. Gohan, Goku, and Piccolo retreat to the mountains to train for the Androids arrival, while Vegeta trains under 450 times Earth Gravity, still trying to surpass Goku. Krillin, Tien, Yamcha, and Choazu train hard for the coming battles. Then after their 3 years of training, the Group of Warriors meets up on an island near where Trunks first arrived. Bulma is there waiting for them, with a baby in her arms!! She tells everyone it is Trunks, the son of her and Vegeta!! Yajirobe shows up in a hovercraft to deliver some Senzu Beans from Karin for the coming fight. Just as he is leaving, Yajirobe's hovercraft explodes (unfortunately he is safe and sound) and the group notices the adroids terrorizing a town nearby. Thus begins the epic battle with the Androids.
The warriors split up to search for the Androids, and Yamcha is attacked and beaten by one of them. Sensing his dying power the others go to his aid. Krillin takes Yamcha to Bulma to get a Senzu Bean, while the rest of the Warrior and the two androids go off to a more deserted place to battle. Goku begins battling with Android 19 and is winning but weakly, and suddenly suffers his heart failure. Android 19 kicks him around for a bit before trying to absorb more of Goku's energy. A revived Yamcha, Krillin, and Gohan tell everyone about the Androids' ability to absorb people's power. Vegeta jumps in and saves Goku. Vegeta powers up into SSJ, to everyone's surprise, and defeats Android 19. Android 20, now realizing that he underestimated the Z Warriors' powers, retreats. Vegeta demands a Senzu Bean to restore his used power, and takes off after Android 20, with the other Warriors right behind him.
Trunks arrives from the future and sees Android 19's head. He realizes that the Z Warriors are fighting the wrong Androids. Meanwhile, Android 20 is surrounded and tries to absorb Piccolo's energy, but Gohan comes to his rescue and Piccolo is given a Sensu Bean to recover. Bulma and Baby Trunks show up with Yarirobe and Android 20 blows up their ship to draw away attention while he made an escape. Trunks saves Bulma and Baby Trunks, and then Bulma tells her story about the Android she saw. She says that Android 20 is really Dr. Gero, the androids' maker. Dr. Gero made Android 19, so that 19 could make Dr. Gero into an Android (Number 20).
The Z Warriors discover that Number 17 and 18 (the real threat) are not awake yet, so they rush to Gero's lab to destroy them. But Gero sees what is happening and head to his lab as well. Gero beats them to his lab, and by the time the Z warriors arrive, the Androids are awakened by Gero and are wrecking their maker's lab. Number 17 beheads Gero and crushes the head. Number 17 and 18 awaken another android, Number 16 and all the Androids and the Z warriors head to a remote area to battle. The androids defeat Piccolo, Trunks, Tien, and Vegeta and then head toward Krillin. They admit to him that it was all just a game and that they would gladly fight their enemies again once they have healed. Number 16 however refuses to fight because he was created only to fight the one called Goku.