This is a hard-cover book with 8 short stories including the story "Riverworld" which started Farmer's Riverworld series. The title story is about a group of aliens who have secretly manipulated the actions of humans to extract a special form of energy. The energy is used to power their spaceship which, in fact, is the entire universe. The stories in this collection were written between 1960 and 1969 and were published in several science fiction magazines at the time. These are great examples of stories written in the second golden age of science fiction which is when I started reading this genre. ( )