The Secret Keepers by Trenton Lee Stewart

Twelve year old Reuben lives in a rundown neighborhood in New Umbra, a town controlled by a powerful and mysterious figure called the Smoke.  Avoiding the henchmen who patrol the city, he finds a pouch containing a unique antique watch with a missing hand.  When he begins asking questions about the device, Reuben attracts the attention of the Smoke who is intent on possessing the device and harnessing its magical powers.  With an inscription on the watch as a clue, Reuben sets out to uncover the secrets of the device while evading the Smoke and his minions.  A stand-alone selection by the author of The Mysterious Benedict Society, this book will be a new favorite of fantasy lovers 11+.