Things will get intense on Friday's all-new episode of "Grimm" as Nick and Hank go on the hunt for a serial killer and Juliette continues down a pathway of destruction and revenge.

In the next episode, which is titled "Headache," Juliette, who seems to have slipped into darkness past the point of redemption, will execute her plan of vengeance after refusing Monroe's and Rosalee's offer to help her.

A preview video also reveals that Trubel will pay another visit to Portland. In addition, Kelly Burkhardt will bring Diana as well. Plus, Wu will get beat down by Captain Renard.

TVLine published a sneak peak from "Headache" that shows that Nick, Hank and Wu will make a surprise visit to Renard's house after a mysterious man answers his cell phone and tells Nick that the captain is asleep in his home. Once the three arrive at his home, they become even more confused when Renard tells them that he was asleep during the whole ordeal.

During an interview with TVLine, series so-creator James Kouf opened up about the Season 4 finale, which will air on May 15, teasing that Nick will come across a discovery that will cause him to seek revenge against the Royals.

According to CarterMatt, the synopsis reads as follows:

"While investigating a grisly murder, Nick (David Giuntoli) and Hank (Russell Hornsby) get closer to uncovering the identity of the serial killer while Wu's (Reggie Lee) life is put in grave danger. Having turned down Monroe (Silas Weir Mitchell) and Rosalee's (Bree Turner) offer, Juliette (Bitsie Tulloch) solidifies a new alliance as she works to get her revenge. Elsewhere, Trubel (guest star Jacqueline Toboni) makes a surprising return to Portland."

"Grimm" Season 4, Episode 21, "Headache," airs on Friday, May 8, at 8 p.m. EST on NBC.

Watch a preview video below: