On Christmas Eve, pickle salesman Jack Polo approaches his front door. Inside in the living room, books fly through the air on their own, Christmas cards fall off the fireplace mantle, and the water in the aquarium boils. Singing cheerfully, Jack comes inside and checks himself in the hall mirror, which cracks. He casually dismisses it as the foundation settling and goes on, unaware that a demonic visage appears in the glass behind him. When he sees the devastation in the living room, Jack says that it must be raccoons that came down the ceiling and promises himself that he'll put a grille in place. He says, "que sera sera," but is briefly shocked when he sees that the fish have boiled to death in the aquarium. However, he soon cheers up and figures that the thermostat is broken. A book flies off a shelf, and Jack picks it up and says he planned to rearrange them anyway.
Jack's daughter Amanda comes to visit and Jack runs to the front door to intercept her. As soon as he leaves, the demon from the mirror appears in the room, snarling and tearing up the couch. In the hallway, Jack tells his daughter that she was supposed to be sending Christmas with her mother and he wasn't expecting her. Amanda wonders if he doesn't want her there, and Jack that she should never doubt his feelings for her. When he says that he decorated the Christmas tree by himself, Amanda goes to the living room to see it and is shocked at the destruction. Jack simply claims that he's clumsy, but Amanda isn't convinced.
Jack takes Amanda to the kitchen for some hot chocolate. As soon as they go through the door, the demon, a Yattering, appears again and scratches the door, snarling. Amanda hears it and comes back out, and notices the scratches. Jack claims that they're old marks and then gives her his Christmas present: a faux pearl necklace. As they hug, carolers come to the door and the Polos go to listen. Once they're gone, the Yattering appears again, groaning in agony at the sound of holy music. He calls to his master, Beelzebub, who appears and tells his minion that he must convince Jack to doubt his faith and renounce God. The Yattering insists that it can't be done, and that Jack didn't break even when the demon tricked him into finding his wife and best friend together in bed. Jack simply said "que sera sera," which Beelzebub recognizes as an ancient invocation of acceptance against misfortune. The Yattering explains that it's done everything possible, up to and including microwaving Jack's cat, but Jack simply won't break. He begs Beelzebub for the chance to touch Jack directly, but his master warns that under the Treaty of Job, any demon that touches a man before he is condemned becomes the man's slave. Beelzebub tells the Yattering to break Jack or suffer in his place, and then departs.
The carolers finish and ask for a donation, which Jack cheerfully provides. He and Amanda go inside and she smells sulphur, but Jack dismisses it as backed up drains. As he picks up his groceries, the bag starts twitching and the Christmas turkey comes to life, flapping its wings and jumping to the top of the Christmas tree. Jack offers his daughter a drink and she wonders how he can accept what's happening. Her father insists that the only possible explanation, that there is a demon, can't be true because there are no such things. When Amanda persists, Jack says "que sera sera" and insists that all he can do is accept whatever will be, and that his philosophy has served him well for the last 50 years.
As Amanda apologizes, the Christmas tree starts to spin. As presents fly through the air, Jack grabs a fireplace shovel and starts swinging wildly until the tree stops. Recovering quickly, Jack tells Amanda that he's fine and invites his daughter to join him in a walk outside. She goes with him and the Yattering appears, biting a present in frustration. Beelzebub returns and warns the demon that he's about to fail, and that Jack is going to visit his wife and forgive him. He tells the Yattering to stop Jack from leaving the house. It goes to the door and closes the bolts, and relocks them when Jack tries to open them. Jack suggests that they both go to the back door and Amanda runs to the back. Fooled, the Yattering goes after her and Jack opens the front door, then tells Amanda that he's succeeded. Frustrated beyond measure, the Yattering grabs Jack... and becomes visible.
Amanda sees the Yattering for the first time and it snarls at her, and Jack tells it to mind its tongue. It obeys him and Jack explains that since it touched the condemned before they were condemned, the Yattering is now his slave. He tells Amanda that her grandmother, his mother, was a witch, and Hell wanted Jack's soul in payment. Jack then tells the Yattering to clean up its mess and make Christmas dinner. The Yattering warns that Jack will never go to Heaven if he has a demon slave. However, Jack just smiles and has the disgruntled demon recite his new master's philosophy: "que sera sera."