Les anciens ennemis

Trunks shows up at Goku's house badly beaten, and a black hole has suddenly appeared in the sky. When he recovers, he explains that Android 17 attacked him, and said that Dr. Gero and Dr. Myuu have demanded that Goku come to hell through the black hole and fight them, or else they will resurrect Cell and Frieza and send them to Earth. A reporter on TV says that there are mysterious monsters destroying the city, and they recognize the monsters as everyone Goku has defeated over the years. Goku decides to go to hell and fight. Down in hell, Dr. Gero and Dr. Myuu explain that they created a replica of the Android 17 on Earth, but altered both of their programming to make them completely loyal. When these two androids fuse together, the resulting Super Android 17 will have unbelievable power. When Goku arrives in hell, Dr. Gero and Dr. Myuu flee, and close up the hole connecting Earth and hell, trapping Goku inside. Cell and Frieza show up, and now that he's trapped in hell, he has no choice but to fight them. (Source: Wikipedia)