In the year 1999, five young men return to Earth after a lengthy space voyage, only to find a planet left in ruins from a worldwide nuclear war. When their ship is captured by an alien craft, they learn Earth has been conquered by the evil Galra Empire, led by the ruthless Emperor Daibazaal. The young men are sent to the Slave Castle, a place where unspeakable horrors await all the races conquered by the Galrans. After a while, the men plan a daring escape from their grisly prison, though no one had ever made it out alive before. Escape is their only option, for staying means certain death for all of them.