Vanity is one of the deadliest sins, and it's one that can get you killed in "Grimm."

The newest episode of "Grimm" season 5 taps into people's desire to look young and attractive. A synopsis for episode 15, "Skin Deep," states that Detectives Nick Burkhardt (David Giuntoli) and Hank Griffin (Russell Hornsby) look into the case of an attractive young woman who appears to have aged 70 years overnight before she died. The two suspect that a Wesen is involved, which leads to Rosalee Calvert (Bree Turner) going undercover to check out the suspect. Meanwhile, Eve (Bitsie Tulloch) goes for a more decisive approach, in order to know more about Capt. Sean Renard's (Sasha Roiz) dealings with Black Claw.

The trailer for the upcoming episode teases viewers with a new and disturbing Wesen. The clip starts with a shot of the crime scene. The body of an old woman is shown, with Nick, Hank, and Wu (Reggie Lee) doing a preliminary investigation. A doctor is shown and he's teased to have "discovered the fountain of youth."

This is followed by a scene showing a woman being treated by him. Some kind of cream is slathered on her face and viewers can see that she has a few wrinkles. She later appears to be giddy with joy at what she sees in the mirror and tells her doctor that "it's a miracle." Unfortunately, that miracle appears to have a price. The man turns out to be a Wesen with tentacle-like appendages where his mouth should be, similar to the creature in the "Predator" movies. He's shown apparently sucking a patient's face off. This doesn't bode well for Rosalee, who's a patient of his. Luckily, Monroe is there to hopefully save the day. The trailer ends with the blutbad barging into the clinic, demanding that the doctor gets away from his wife.

Monroe and Rosalee have been getting quite a lot of screen time in the past episodes, much to the delight of their fans. However, a lot of viewers are flabbergasted that after everything Nick and Monroe went through in the Keys story arc, the show's writers have opted to just literally hide the mysterious stick and go back to the ongoing Wesen uprising and Renard's quest for power.

Renard's recent actions have also raised a lot of eyebrows and red flags among fans. It seems that the captain's quest for power would soon have him stooping to new lows, even to using his daughter. Roiz admitted as much to TV Line and said Diana is more than just a daughter.

"She is definitely a very strategic pawn in this whole mythology," Roiz explains. "She's proven to be someone who's gifted and has a significant amount of power."

"Grimm" season 5 will be airing its latest episode on April 1.