Tim Waggoner 
The Killing Time [EPUB ebook] 

A brand-new original novel based on the hit NBC series. There once was a man who lived a life so strange, it had to be true. Only he could see what no one else can: the darkness inside, the real monster within. And he’s the one who must stop them. This is his calling. This is his duty. This is the life of a Grimm. A mysterious creature stalks the streets of Portland, looking for a new identity. With one touch it can dissolve its victim, assuming their appearance, personality, and memories. When Portland homicide detectives Nick Burkhardt and Hank Griffin are called in to investigate a bizarre murder, Nick comes face to face with the changeling, but its powers have an unexpected effect on the Grimm, unleashing a deadly Wesen plague and untold chaos.