A millennium into the future, two advancements have altered the course of human history: the colonization of the galaxy and the creation of the positronic brain. Isaac Asimov's Robot novels chronicle the unlikely partnership between a New York City detective and a humanoid robot who must learn to work together. Like most people left behind on an over-populated Earth, New York City police detective Elijah Baley had little love for either the arrogant Spacers or their robotic companions. But when a prominent Spacer is murdered under mysterious circumstances, Baley is ordered to the Outer Worlds to help track down the killer. The relationship between Baley and his Spacer superiors, who mistrusted all Earthmen, was strained from the start. Then he learned that they had assigned him a partner: R. Daneel Olivaw. Worst of all was that the "R" stood for robot---and his positronic partner was made in the image and likeness of the murder victim!

This book is the fourth of six that describe mysteries solved by the Black Widowers, based on a literary dining club he belonged to known as the Trap Door Spiders. It collects twelve stories by Asimov, together with a general introduction and an afterword following each story by the author. Nine of the stories were previously published; "The Driver," "The Wrong House" and "The Intrusion" are new to this collection. Each story involves the club members' knowledge of trivia. Nearly every story here is about decoding a riddle, each of which provides a clue based on dying or last words, misunderstood words, forgotten words, or withheld words. A few are based on facts that are, perhaps, not generally known to the public Asimov was a frequent writer of popular science and his inclination to explain anything and everything for the general public carried over into other fields, such as history and sociology but all the mysteries play fair with the reader, who is given either enough information to figure out the solution or a satisfying conclusion that is based on previously given facts and personality qualities.