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.Contents1. Introduction2. Sixty Million Trillion Combinations3. The Woman in the Bar4. The Driver5. The Good Samaritan6. The Year of the Action7. Can You Prove It?8. The Phoenician Bauble9. A Monday in April10. Neither Brute Nor Human11. The Redhead12. The Wrong House13. The Intrusion