Mitch Pileggi as Skinner
Mulder (David Duchovny) and Scully (Gillian Anderson) try to track down Skinner (Mitch Pileggi) after he goes AWOL in Season 11, episode 6 of Fox’s “The X-Files.” Fox/Shane Harvey

Mulder and Scully try to locate Skinner in tonight’s episode of “The X-Files.”

According to the synopsis for Season 11, episode 6 of the Fox series, Skinner (Mitch Pileggi) goes AWOL when his past comes back to haunt him. As Mulder (David Duchovny) and Scully (Gillian Anderson) look for him, the pair’s growing mistrust of the assistant FBI director reaches its peak.

In the trailer for the episode, Alvin Kersh (James Pickens Jr.) tells Mulder that Skinner “is poking around in places he shouldn’t be poking.” While the reason behind Skinner’s sudden MIA is unclear, Scully suspects that it’s something to do with Skinner’s time in Vietnam.

In the promo clip, Skinner is seen checking out an abandoned house in the middle of the woods. And at the end of the video, Skinner appears to have fallen into a trap with new character Davey James (Haley Joel Osment) finding him in a pit.

Written by Gabe Rotter, the episode focuses on Skinner’s backstory and features flashbacks to his time in Vietnam. In addition to filling in some holes regarding his stint in the Southeast Asian country, Pileggi told TV Insider that episode will make the viewers “understand why Skinner behaves the way he does.”

“You’re going to find out a lot more about his past,” Pileggi told TVLine of the Skinner-centric episode last October. “Fans will find out who he is, where he comes from and why he is the way he is.” The actor went on to say that the hour will reveal that his cranky FBI boss is more than just the guy “who sits in the office grumbling at Scully and Mulder. “Ultimately, he is their champion,” Pileggi said of his role.

In addition to Pickens and Osment, also guest starring in the episode are Jovan Nenadic as John “Kitten” James, Brendan Patrick Connor as Sherriff Mac Stenzler, Jeremy Jones as Sergeant, and Cory Rempel as young Skinner.

“He threw himself into it,” Pileggi said of Rempel, who happens to be his nephew by marriage. “I got a text from him at the end of his first day of filming, saying, ‘That was probably the best day of my life.’”

“The X-Files” Season 11, episode 6, titled “Kitten,” airs tonight at 8 p.m. EST on Fox.