Ripper

Fiction by Isabel Allende.

http://www.barnesandnoble.com

This book is not about Jack the Ripper, except in a very peripheral way.

Instead it's about some teenagers who play a "game" called Ripper, in which they try to solve real-life murders. (They apparently began with the Jack the Ripper murders in a minor backstory.)  It helps that one of the teens is the daughter of the police chief investigating said crimes.