"Criminal Minds" season 12 is currently on a two-week hiatus, but when it returns to the small screen, the team will be in the Halloween spirit.

For episode 4 titled "Keeper," the Behavioral Analysis Unit (BAU) will be after a serial killer hiding along the Appalachian Trail in rural Virginia.

Time is of the essence for this search as the murderer is serious about doubling his body count. As revealed in the "Criminal Minds" season 12 episode 4 promo, seven people have already been slaughtered by the killer on the loose.

The BAU are putting themselves in grave danger just going to the woods, which is the territory of the killer, who appears to have long, sharp nails and knows the area extremely well.

This case will be the first one without Hotch (Thomas Gibson) and with Emily Prentiss (Paget Brewster) taking over, which means that fans could be in for something new.

Brewster was only meant to star in several episodes of "Criminal Minds" season 12. However, the exit of Gibson, which was prompted after his altercation with a producer, led to her being a series regular again.

The actress was a regular in 2012, but then she was not that involved on the show especially in the recent years as she starred in a new one, "Grandfathered."

The show was canceled after one season, though, clearing Brewster's schedule and allowing her to be a bigger part of "Criminal Minds" season 12.

Explaining what her character has been up to during the time she was gone, the star told CBS News, "She's been running Interpol for four years, and now it's just really nice to be back on the team full-time."

"So far, they've made [Prentiss] powerful and good at the job and invested," she went on to say about her character. Indeed, "Criminal Minds" season 12 episode 4 will see her in charge.

"Criminal Minds" season 12 episode 4, "Keeper," is scheduled to air on Wednesday, Oct. 16, at 9 p.m. ET on CBS.