Here's the official guide of Grimm season 2 episode 19 "Endangered". this episode airs on Friday, April 26 on NBC.

NICK FACES AN OTHER WORDLY MYSTERY THAT MAKES HIM QUESTION WHAT HE KNOWS ABOUT THE WESEN WORLD --

• Mysterious cow mutilations and reports of glowing creatures put Nick (David Giuntoli) on a case that forces him to question the existence of aliens within the Wesen world.
• He also meets a strange UFO expert who seems to know more than he’s letting on.
• Meanwhile, Nick digs further into the key, and Juliette’s (Bitsie Tulloch) romantic memories of Nick start coming back in a big way.

Source: NBC