Android 18 is at Satan's house demanding for the money Satan promised to give her for letting him win the World tournament. Then, one of Satan's disciple's minion arrives and blackmails Satan. He states that if Satan doesn't go with him to fight (test) some bio-warriors, he will tell the press that Satan wet his bed up to the 6th grade. Android 18 tags along to follow Satan and Goten and Trunks hide in the trunk of the car to secretly follow.
Goten, Trunks, and Android 18 easily trash the bio-warriors. The battle room opens to reveal a bio-warrior creation laboratory. Goten and Trunks explore and fight a shocking experiment- the creation of a clone of Brolly! (Kitou-shi of Movie 10 had taken samples of Brolly's blood and sold them to the lab for money. Brolly's DNA was studied and now Brolly was cloned.) Goten and Trunks attempt to do fireballs to destroy the developing creation, but Brolly awakens too early. Much fighting occurs. Chemicals pour over the Brolly clone so that the clone now looks like he's melting. Trunks tricks Brolly into melting into the chemicals. Much of the lab is destroyed, and most of the employees of the lab are killed in the spilling chemicals.
At the end, Goten, Trunks, Android 18, Krillin, Satan, and a few scientists escape from the lab. Our heroes observe that water hardens the chemicals that are pouring over the city-island. Goten, Trunks, and Krillin fly up and go fireballs on the sea. The sea water splashes over the island and the city is saved. The Brolly clone, now bigger that ever because the chemicals combined with his chemical body, appears out of the sea. After giving everyone a scare, the clone hardens. Goten and Trunks destroy the stiff clone. There is peace again, but Satan is trying to swim home rather than having to pay Android 18 for rescuing him.