S6E6 · How the Ghosts Stole Christmas

Dana Scully (Gillian Anderson) reluctantly responds to Fox Mulder 's (David Duchovny) call on Christmas Eve to investigate a haunted house in Maryland. He explains that during Christmas of 1917, a young couple living in the house agreed to a suicide pact, one killing the other and the remaining one committing suicide. He explains that they could not stand the thought of being alone after the other died and during the afterlife; they wanted to spend all of eternity together. Now, Mulder claims, they haunt the house every Christmas Eve.

Scully, who doesn't want to abandon her Christmas plans, follows Mulder into the house to retrieve her car keys from him, and the door to the mansion slams shut. Inside the house, the agents experience strange phenomena: creaks are heard in the ceiling from the upper floor, and the shadow in the form of an old woman in a nightgown is seen, among other occurrences. Mulder and Scully reluctantly decide to investigate the floor above them. There, they find a massive library storing two corpses that have the same clothes and hairstyles as the agents, along with two gunshot wounds. They decide to search other rooms, only to find that every door they walk through is the same library room they first entered. They then decide to split up, hoping to find a way out of the room.

While separated, the agents meet the inhabitants of the mansion—Maurice (Ed Asner) and Lyda (Lily Tomlin). The ghosts soon turn the agents against each other. Scully is told that Mulder will kill her. Scully meets back up with Mulder, only for him to pull out a gun and shoot her. Scully, completely confused, loses consciousness, and the perspective shifts. It is revealed that Lyda is actually the one carrying out these actions and, through her ghostly ability to create apparitions, causes Scully to see Mulder instead. Meanwhile, Mulder comes upon a bleeding Scully lying on the floor. When he leans over her to try to help her, she shoots Mulder. Again, the audience sees that it is Lyda pretending to be Scully, manipulating Mulder.

Both Mulder and Scully stumble down the stairs in hope of just getting outside to die. They meet up by the door, both crawling on the floor, covered in massive amounts of blood. Scully claims he shot her, while Mulder claims she shot him. Mulder realizes that that could not have happened and stands up. The illusion is broken, and the two leave the house. Maurice and Lyda sit by the fire, holding hands, saying that they almost had the two agents. Meanwhile, at Mulder's apartment, Mulder and Scully exchange gifts, even though they told each other they would not.