On the night before Christmas, Mulder convinces Scully to put aside her gift wrapping and stake out a reputed haunted house. But they discover a married couple living in the house, keeping a secret the agents never expected.

It's late Christmas Eve. Telling tales of star-crossed lovers who forged a pact to be together for eternity, Mulder lures Scully into the darkened mansion that the ghost couple purportedly haunts. Once inside, the front door locks behind the duo and traps them inside. Mulder believes it is the work of the ghosts who inhabit the house. Scully, ever the skeptic, instructs Mulder on the psychology of peoples' need to believe in the afterlife as a means to satisfy their fear of mortality. But when a previously locked door springs open and a light shines from inside the room beyond, Mulder chalks it up to ghosts. Scully, admitting that she is afraid but that it's an irrational fear, still sticks with the belief that people might be actually living in the house.

Passing through the door, the partners find themselves in a library. And in a series of odd twists and turns, they become separated -each trapped in some parallel universe version of the library. It is here that Mulder meets Maurice The Ghost , who convinces Mulder to shoot Scully. In her own parallel library, Scully meets Lyda The Ghost , who convinces Scully to shoot Mulder. When the two agents meet back up, they follow through on the ghosts' mischievous plan and fire their weapons on each other. As they lay gasping on the staircase landing, they realize it was only some kind of mind trick played on them by the ghosts.

Safely ensconced back in their homes, the duo agree that the events of the evening never happened.