Excellent book for an excellent game system. This is the second edition of "New" World of Darkness, now called Chronicles of Darkness (it also has the God-Machine aspect of the game added in). You don't need this book to play the supernatural lines, but it nevertheless is a handy reference to any of the Chronicles of Darkness splats (e.g., Werewolf: the Forsaken, Geist: the Sin-Eaters, etc.). However, it's also a wonderful gem for running a "mortals" story within the world. Half the fun of this book is having the ability to play as a bunch of normal(ish) people who happen to stumble upon some dark, supernatural, creepy things.
This rulebook includes mechanics for a number of competitive aspects/encounters you may find in a game. Combat is an obvious inclusion, but this system also has mechanics for social competitions, investigations, and more. The system is also what they descibe as a toolbox, meaning if you would rather just play something by ear, you can do just that. You can remove or add in elements as you desire. For example, don't want the social maneuvering rules? You don't have to use them. (That said, I think they make a fine addition to the game.)
Ultimately, if you enjoy World of Darkness/Chronicles of Darkness, I recommend giving this book a try.
[5 of 5 Stars!]