Sarah Jeffery and Madeleine Arthur have landed guest starring roles in Fox’s “The X-Files.”

Jeffery and Arthur will appear as Brianna Stapleton and Sarah Arthur, respectively, in Season 11, episode 5 of the sci-fi series. According to the synopsis for the episode, Briana and Sarah are two teenage girls who attack one another as each one of them believes that the other is a monster. Mulder (David Duchovny) and Scully (Gillian Anderson) investigate the case and realize that it could be connected to their long-lost son William.

In the trailer for the episode, Mulder, Scully and Skinner (Mitch Pileggi) go to an abandoned ship where Brianna and Sarah attack each other. But for some reason, Skinner wants Mulder and Scully to stop working on the case.

“Drop this investigation,” Skinner tells Mulder.

“This is where it all started,” Mulder replies.

“You’re wrong. This is the end of the road,” Skinner says.

Elsewhere in the promo clip, Scully seems to be dreaming of a young man in a hood who breaks into her place. Although Scully doesn’t get to see the man’s face in her dream, she is quite sure that it’s William. “It’s William, our son. He wants us to find him,” Scully tells Mulder in the trailer.

Later in the video, a young man, who appears to be William, unzips himself out of a body bag. Mulder and Scully seem to be looking for him in the hospital but Scully gets shot during the process.

Jeffery currently plays Cristina Santos on NBC’s “Shades of Blue.” Her other TV credits include Audience Network’s “Rogue,” Fox’s “Wayward Pines” and Disney Channel’s “Descendants.”

Arthur, meanwhile, is best known for her role as young Willa Warren on ABC’s “The Family.” She currently portrays the role of Fray on Syfy’s “The Magicians” and is set to appear in the midseason premiere of “Legends of Tomorrow.” Arthur also guest starred on AMC’s “The Killing” and CW’s “The Tomorrow People” and “Supernatural.”

In addition to Jeffery and Arthur, also guest starring in the next episode of “The X-Files” are William B. Davis as Cigarette Smoking Man; Miles Robbins as Jackson Van De Kamp; and Louis Ferreira as Detective Costa.

“The X-Files” Season 11, episode 5, titled “Ghouli,” airs on Wednesday, Jan. 31 at 8 p.m. on Fox.