Updated and Revised 2nd edition. A Guide to Deduction is a guide for any potential Sherlock Holmes or John Watson. A series of reflections on subjects to help anyone from novices to experts to learn how to deduce things from your surroundings. The book is a useful reference to learn about the common details that appear in the mysteries of Sherlock Holmes. In this second edition, learn more about lock picking, poisons and the chemistry in the world around us.