Trurl and Klapaucius come to a planet ruled by a king who loves hunting. He has already "conquered" all the most dangerous of predators, and now hires constructors (engineers) to make new, mighty robotic beasts for him to hunt. He has already executed all of the previous constructors who visited because they could not build beasts that would be challenging enough to hunt. When the two famous Constructors arrive, they are arrested and ordered to construct a worthy foe for the king within twelve days.