I have yet to try the actual game rules, but I would recommend this book to anybody running any kind of investigation style game in any system at all. The back half of the book is filled with an excellent set of system-agnostic tables which can be used to quickly generate a setting and investigative mysteries within that setting. I went from having no idea what the mystery would be three hours before the first session to having a fully fleshed out mystery by the time we started thanks to this book.

It's not just the idea of using tables to generate investigative scenarios, but also the fact that the tables and structure are unusually well thought out and evocative, and fit together in clever, helpful ways. An excellent resource for any GM interested in the genre.