Grimm Season 1 Episode 21 (05/11/12)
Nick and Hank investigate the ruthless murders of two men in the woods after Juliette stumbles upon the bodies while helping a patient.
It turns out a Wesen therapist developed a drug that keeps Wesen forms and urges under control, but if the dosage runs low those urges come back and the patient is unable to transform back to human form.
Nick confronts the doctor, who is also on the drug. He's unable to control his actions and attacks Nick and Hank. Hank is able to rescue Nick but not before getting a good look at the doctor's Wesen form.
Meanwhile, Juliette is analyzing some hair she found on one of her pet patients and analyzes. It's not known to man, as it is half human/half animal. She tells Nick about it, and tells him she wonders if the stories and fairy tales they hear as children are actually true.