"Kitten" is the sixth episode of the eleventh season of The X-Files. It is directed by Carol Banker and written by Gabe Rotter.
Skinner goes AWOL when his past comes back to haunt him. As Mulder and Scully try to track him down, their growing mistrust of him reaches its apex.
In 1969, during the Vietnam War, a platoon of U.S. Marines including Walter Skinner and John "Kitten" James, are tasked with escorting a crate marked MK-NAOMI to a rendezvous point. They come under enemy fire as they reach the landing zone and are forced to take shelter with a group of civilians in a hut. As Skinner doubles back to help a wounded soldier, the crate is damaged by gunfire and Kitten is exposed to a yellow gas. When he returns to the hut, Skinner finds Kitten has murdered the civilians.
In 2018, Mulder and Scully are called before FBI Director Alvin Kersh, who questions them about Skinner's whereabouts. Skinner has vanished without explanation, prompting Mulder and Scully to investigate his apartment. There, they find Skinner was mailed a severed human ear. Mulder identifies the parcel as coming from the town of Mud Lick, Kentucky. During their journey to the town, Scully realizes that Skinner's service record and the records of his platoon are classified as top secret.
Arriving in Mud Lick, Mulder and Scully find a body in the morgue missing an ear. While Mulder identifies the cause of death as being a punji stake—a Vietnam War-era booby trap—Scully questions the local sheriff about a mass hysteria gripping the town amid claims of a monster lurking in the nearby woods and people losing their teeth without explanation.
The body of Banjo, another Vietnam veteran, is found the next day at the bottom of a punji pit. A nearby camera, supposedly used to monitor deer in the area, has recorded Banjo's death and Skinner is seen approaching the pit shortly after Banjo fell in. Mulder and Scully lose the support of local authorities when they admit Skinner is their boss, and are unable to convince the sheriff that he is innocent. Mulder continues to watch the video and sees a hooded and cloaked figure lurking in the woods: the "monster" terrorizing the town, which Mulder immediately dismisses as a person in a costume.
Skinner approaches Davey James, Kitten's son, in his hunting cabin. Davey accuses Skinner of failing to help Kitten. After his exposure to MK-NAOMI, Kitten became increasingly violent and was court-martialed upon his return home. He was committed to a mental health facility outside Mud Lick, with Skinner's testimony key to imprisoning him. Davey reveals that all of the soldiers exposed to MK-NAOMI were sent to the same facility, where the experiments continued, implying that Kitten's initial exposure was orchestrated by the government. Initially an attempt to turn soldiers into more efficient weapons of war by channeling their fear into aggression, the scope of MK-NAOMI was expanded to become a means of controlling peoples' minds.
Skinner asks Davey to take him to Kitten; Davey leads him to a tree where Kitten hung himself after leaving the facility. As he approaches Kitten's body, Skinner falls into another punji pit and is impaled on a spike. Davey abandons him as Mulder and Scully arrive, having looked into Vietnam veterans in the area. Davey claims no knowledge of Skinner and starts ranting about a government conspiracy to control the population with MK-NAOMI, which he claims is a perfected version of MK-ULTRA. The agents ostensibly accept his explanation and leave, but Mulder suspects Davey after noticing photos of Kitten and Skinner in his cabin. He doubles back and investigates the cabin, finding the "monster" costume from the video. A search of the area leads him to Skinner in the punji pit. Davey attempts to ambush them, but is caught and killed by one of his own booby traps.
Mulder and Scully ask Skinner about Kersh's claim that they were responsible for his lack of career advancement. Skinner admits that his experience with Kitten and MK-NAOMI in Vietnam shook his faith in the government, but their willingness to pursue the truth wherever it takes them restored his faith in people. He resolves to return to Washington and use his position to fight the government's abuse of power. As Skinner leaves, one of his teeth falls out, implying that he has been exposed to MK-NAOMI.
In the epilogue, a crop duster is seen spraying a field with a yellow gas as Davey's warnings about government conspiracies are repeated in voiceover.
- James Pickens, Jr. reprises his role as Alvin Kersh for the first time since the original series finale, "The Truth". It also looks that he is against agent Mulder again despite the fact that he went over to his side at the end of the mentioned episode.
- The episode is devoted to the backstory of Walter Skinner. "We learn more about Skinner and more about his connections to Mulder and Scully and how he’s been a loyal advocate of theirs at his own expense. We learn about his young life and the X-Files moment he experienced as a much younger man."
- The music heard as Mulder and Scully enter the mortuary is reminisant of that heard in Anasazi.
- David Duchovny as Special Agent Fox Mulder
- Gillian Anderson as Special Agent Dana Scully
- Mitch Pileggi as Assistant Director Walter Skinner
- James Pickens Jr. as Alvin Kersh
- Haley Joel Osment as Davey James
- Cory Rempel as young Walter Skinner
- Jovan Nenadic as John "Kitten" James
- Brendan Patrick Connor as Sherriff Mac Stenzler
- Patrick Keating as Begger
- Johnson Phan as Quon
- Jeremy Jones as Sergeant