Nick (David Giuntoli) and his team will be horrified when the mythical Rat King comes to Portland, while Trubel (guest star Jacqueline Toboni) will end up in some big trouble in Friday's episode of "Grimm."

A synopsis for the upcoming episode, which is aptly titled "The Rat King," reveals that Portland will come under attack by an overgrown rodent. In addition, Trubel will be hospitalized after suffering from multiple injuries.

"Nick and Hank (Russell Hornsby) are called to the scene when three Wesen go out on a hunt at a local dump and get more than they bargained for when two turn up dead after they encounter the mythical Rat King. Meanwhile, a very badly wounded Trubel is taken to the hospital and Nick finally meets Meisner (guest star Damien Puckler)," the synopsis reads, according to CarterMatt.

NBC also released a sneak peek video via TVLine that raises several questions about Trubel's return to Portland and her real identity. In the video, Nick tells Wu (Reggie Lee) and Hank that he found Trubel in a badly beaten state and took her to the hospital. Wu and Hank then reveal that the young Wesen fighter has a fake driver's license and a false name. It also turns out that she's been riding around on a pricey motorcycle worth at least $30,000.

"Scream" actress Carlson Young will also guest star in the episode, notes TVLine.

Later on in the season, executive producer Jim Kouf teased that fans can also look forward to learning more about the origins and whereabouts of the mysterious keys in the 100th episode, which is titled "Into the Schwarzwald." It will air as Episode 12 in 2016, according to Movie Pilot.

"Grimm" Season 5 Episode 4, "The Rat King," premieres on Friday, Dec. 4 at 9 p.m. ET on NBC.

Watch the preview video below: