The killing time (Grimm #3)

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.