In Ft. Lauderdale, Florida, lightning blows out the lights at an overly-decorated Christmas house. As Pete and Myka arrive, posing as power & light workers, a reindeer slams through the front door. The agents complain that they can't have a normal Christmas, and an animated string of Christmas lights wraps around Pete's legs. As Myka climbs up to the roof to try to recover the artifact, the reindeer's nose on a roof ornament, Pete grabs onto a Christmas statue of a choir boy. It comes to life and attacks him, while the Santa statue on the roof whips Myka. Myka pulls the artifact nose off of the reindeer just in time and neutralizes it, causing everything to revert to normal. A young girl, Catie, runs out to get her dog, which was transformed into the reindeer. When Catie's parents come out, Pete and Myka cover for what happened. Catie gives Pete a candy cane in return for saving her dog and he thanks her.
At Warehouse 13, Claudia tries to give Artie a new jacket for his trip to Las Vegas with Vanessa. Pete and Myka arrive with the artifact while Artie complains that he doesn't have enough time to go with Vanessa. He tells them that his father called and guilted him into coming with them, and Hugo found out about it and he's coming as well. Artie offers to go with Claudia, but she doesn't want him to be discussing science with her brother during their sledding trip. When Artie tries to convince Pete to let him do Warehouse duty instead, Pete refuses and Myka offers to take Artie with her. However, when she suggests that Vanessa could get involved with Hugo, he reluctantly agrees to go on the Las Vegas trip.
Pete heads to the Christmas aisle of the warehouse and puts away the reindeer nose. He slips on the snow and several artifacts land on him. Pete puts them on the shelves and goes back to the office, and finds two strangers there, a man and a woman. They draw Teslas on him and demand to know who he is. Pete asks where Artie is, and James MacPherson comes in and says that Artie hasn't worked there in a long time.
The warehouse agents handcuff Pete, who Pete explains that the last time he saw MacPherson, he had died at the Escher Vault. MacPherson is willing to give Pete the benefit if he knows Artie. They wonder how Pete broke in but Pete insists that MacPherson turned evil. When they prepare to take him to the B&B, Pete says that Leena can identify him. The male agent, Raymond, takes Pete there but Leena has no idea who Pete is. However, she can tell that Pete has no aura. When Raymond's partner Sandra calls him to explain that no Pete Lattimer has shown up on the databases, Pete knocks Raymond out, grabs the agent's Tesla, and holds off Leena while he frees himself. He insists that MacPherson is using artifacts to whammy everyone, tosses Leena the Tesla, and runs off to find someone to help him. He's unaware that Mrs. Frederic is in the other room, listening.
Pete calls Mrs. Bering at her bookstore and introduces himself as Myka's partner. However, she has no idea who Pete is or what Edgar Allen's pen is. He asks for Myka but Mrs. Bering says that Myka hasn't been there in two years since her father died. Pete is surprised to learn that Warren is dead and insists that he's still alive, and Myka's mother hangs up.
In Washington, Myka is working at her Secret Service office when Pete comes in and flashes a stolen badge. She also has no idea who Pete is and has never heard of Warehouse 13. Pete tells her everything that he knows about her personal life but Myka figures that he's a stalker and insists that she would remember him if he was her partner. He begs her to listen but she asserts that she would never live in South Dakota and figures that Pete is crazy. She has already hit the silent alarm and security guards haul him away.
Back at the warehouse, Raymond informs MacPherson that Pete had military training but his boss isn't impressed. MacPherson sends Sandra to find Pete, much to Raymond's disgust.
Myka is at a bar working when Pete follows her in. She grabs him and slams him onto the bar, and warns him that she can easily shoot him. Pete agrees to leave her alone if she answers one question. Myka lets up and Pete asks her why she's spending Christmas Eve alone when he knows that she has people who love her. His former partner insists that she has people that love her but can't name a single one, and Pete says that his Myka loves working in a warehouse because she knows the world is filled with endless wonder. Myka says that she's done and starts to walk away, and Pete tells her that in his reality, Warren Bering is still alive and spending time with his daughter. He tells her about the book that he wrote, The Blue Willow Sky, and how her mother burned it. Myka realizes that he's telling the truth and agrees to help him. When Pete says that they have to find Artie Nielsen, Myka knows him as Arthur Weisfelt.
Pete and Myka go to the federal correctional facility where Artie is being held after Myka put him there. He doesn't remember Pete but is familiar with Myka, who points out that Artie tried to assassinate the President. Artie insists he was trying to recover the Bloodstone three years ago, and Pete explains that he met Artie for the first time during the Bloodstone mission. He tells Artie that he's worked at Warehouse 13 with him, and Artie assumes that he's affected by an artifact. Pete tells him what happened and Artie realizes that he touched an upholstery brush. It's Philip Van Doren Stern's upholstery brush, and Myka explains that Stern wrote The Greatest Gift, the story on which It's A Wonderful Life was based. Artie explains that if Pete touched the brush, then he was literally swept away and was never born. Pete insists that he's alive and saved the world, but the candy cane he got from Catie has disappeared because the recovery never happened. Artie figures that when Pete ceased to exist, Artie went to jail and MacPherson convinced the Regents that he was rehabilitated. He also realizes that Pete helped mend the relationship between Myka and her father, which improved his health and kept him alive. She doesn't believe it but they point out that she has to release them.
Myka talks to the warden and tries to get Artie remanded into her custody. He refuses but receives a message saying that someone higher up, a Mrs. Frederic, has had Artie released into Myka's custody for 24 hours. As they leave, Artie explains that MacPherson injected him with a serum that reacts to the painite in the warehouse paint. When Artie warns that no one has ever broken into Warehouse 13, Pete asks if he remembers Claudia Donovan.
At the warehouse, MacPherson is going through the list of artifacts in the Christmas aisle when Raymond reports that Artie was released from prison thanks to Mrs. Frederic's intervention. MacPherson tells Raymond to work with Sandra and bring back Artie, dead or alive.
Artie takes Pete and Myka to the Midwest Psychiatric Clinic and warns that Claudia may remember him. Artie goes in and discovers that she's papered her room with data on Artie. Claudia locks the door behind him and shocks him with an electrical lamp. She demands that he help return his brother Joshua. Pete, hearing her from outside in the hallway, calls to her that Joshua is trapped in an interdimensional void and they know how to get him back. Claudia is surprised that Pete knows about Joshua, and he assures her that they can save Joshua if she'll help them break into Warehouse 13. She agrees in return for Joshua and Pete agrees.
As the reformed team heads out, Sandra and Raymond arrive. Everyone runs for it, splitting up, and Raymond and Sandra split up as well. Pete and Myka manage to knock out the warehouse agents all and Myka calls Pete partner.
At Warehouse 13, Mrs. Frederic comes to see MacPherson and asks why he pulled his agents from the hunt for Shakespeare's Lost Folio. She also wonders why she wasn't notified about Pete, and MacPherson uses DeMille's Riding Crop to paralyze her. He then places her in the bronzer and says that he has no choice because she trusted Artie more than him. MacPherson bronzes her and then receives a transmission from Sandra and Raymond, telling him that Pete and the others escaped. He orders them back to the warehouse, claiming that the building is under attack.
Pete and the others go to the B&B and look for the necklace that will protect Artie from the effects of the painite. Leena catches them, armed with a Tesla, and Artie tries to get through to her, asking her to trust him. She admits that she could feel that something wasn't right and welcomes Artie back, and then gives him the protective necklace.
The team approaches the warehouse and Pete explains to Myka that she knew H.G. Wells and smuggled her out through a secret entrance. Artie finds the hidden entrance, originally from Warehouse 9, and Myka knows how to speak the proper words in Arabic. Claudia hacks the electronic lock and reminds Artie of what he did to her brother, but tells him to save it until later. She gets the door open and runs down the tunnel ahead of the others. There are three doors, and Artie warns that only one of them is safe. Pete gets a vibe from the right door and goes through safely.
As they get to the warehouse, Myka and Claudia look at the artifacts for the first time. Claudia wants to find the compass she needs to bring back her brother, but Pete tells her that they're family and work there every day in a place of endless wonder. Artie directs Pete and Myka to the Christmas aisle to get the brush while he and Claudia go to the office computers and figure out how to reverse the effect. Pete and Myka head down the aisles but find themselves trapped in an endless corridor trap set by MacPherson.
At the office, Claudia hacks the computers and Artie warns that he set up the firewall. She quickly gets in and Artie directs her to the proper files. However, they discover that the brush is missing. Artie catches a glimpse of something flickering and out of the corner of his eye and pulls Claudia away just as MacPherson appears, wielding the samurai sword. When Artie and Claudia try to run away, Sandra and Raymond capture them at gunpoint.
Myka wonders how they escape from artifact traps and Pete says that they break them or outsmart them. She gets an idea and explains that they're trapped in a lemniscate. If they both move as fast as they can in opposite directions, they'll snap themselves out of it. The partners do so and the lemniscate finally snaps, releasing them. They get to the Christmas aisle only to discover that every artifact is missing.
Pete and Myka go to the office and realize that MacPherson has their friends. Using the binoculars, he spots MacPherson and his people taking Artie and Claudia to the bronze Sector. They take the wire across the Warehouse.
As Raymond and Sandra prepare to bronze Artie and Claudia, Artie tries to get through to Sandra and insists that he didn't run the place on blind obedience. As they're sealed in the bronzing canister, Claudia thanks Artie for saving her from MacPherson earlier. He tries to assure her that bronzing isn't painful but isn't very convincing. Outside, Pete uses the cane to shake the floor, and Myka takes out the stunned agents. He frees Artie and Claudia and they realize that Mrs. Frederic has been bronzed. As they head back to the office, Artie explains that Pete needs to touch the Stern Brush again to reverse the effects. MacPherson will try to make the new reality permanent by destroying the brush, and Artie figures that he's use the Lehmann Fornax, the warehouse's furnace powered by the Earth's super-heated core.
The team arrives in the Fornax and find MacPherson hauling a bag of artifacts toward the furnace. Artie tells them to distract MacPherson while he gets behind him. When they reveal themselves, MacPherson locks the door and opens the floor panel, revealing the furnace below. He starts tossing artifacts in and thanks Pete that his sudden appearance brought things to a head between him and the Regents. Artie uses the Lenape Cloak to sneak up on MacPherson and attack him, and the two men struggle on the catwalk. As they fight, the brush falls out of the bag to the edge of the catwalk. Artie grabs it but MacPherson attacks him and prepares to rip off the necklace. With no time left, Artie tosses the brush into the furnace. MacPherson rips off the necklace and Artie dissolves into dust. Pete, taking a leap of faith, leaps into the furnace and grabs the brush in mid-air. As he plummets into the superheated magma...
...reality reverts to what it was and Pete is back in the Christmas aisle. He tosses away the brush and finds Catie's candy cane in his pocket, and collapses in relief. Pete then starts making snow angels as Trailer arrives and licks his face.
Pete goes to the B&B where everyone has gathered because they're snowed in due to the blizzard. Pete hugs Myka and is happy to tell her that her father is still alive. He talks about everything that happened in the alternate reality without his existence. Pete even gives Mrs. Frederic a hug but quickly realizes that he crossed the line. Myka asks if her partner is all right and Pete say that he's glad to be alive and really loves them all. They tell him to stop being a sap and tune the TV into the Christmas Eve boxing match in Vegas… only to discover it's been preempted by a showing of It's a Wonderful Life.