When Dr. Gero was killed by Android 17, he had three other androids stored in the floor below. His death brought to the life Androids 13, 14, and 15. Androids with the sole purpose to destroy Goku.
Goku and his friends are at a mall. Everyone is eating lunch. Meanwhile, Androids 14 and 15 enter the mall and destroy everything in their path. Together, they do a fireball and destroy the portion of the mall where Goku is. Goku and his friends carry all the civilians away from the explosion to safety. Goku encounters Androids 14 and 15 and they battle. Trunks joins the battle. Goku and Trunks lure the androids to the glaciers so that no civilian would get hurt. Gohan and Krillin follow as well, but they only hide and watch. There, Android 13 makes his appearance.
Piccolo and Vegeta also enter the battle. Trunks destroys Android 14 and Vegeta destroys Android 15. However, components from these androids flow up and combine with Android 13's body. Android 13 morphs into a super android and beats up everyone. Finally, Goku creates a Spirit Bomb and uses the fireball's energy to kill the android. After his death, Dr. Gero's computer shuts down.