Since Pete and Myka are heading to their respective homes for Christmas, Claudia beams her holiday cheer at her brother, Josh, and Artie, who "Bah, humbugs" it off with a shrug. But Claudia will not be dismissed so easily: she discovers Artie's happiest moment ever - the time he spent at his family's piano as a child - and sets about finding that very piano to bring home.
But Pete and Myka are stopped in their tracks when Artie delivers the news that a man in Los Angeles named Larry Newly was attacked in his home by a Santa Claus lookalike who whooshed up the chimney as a sparkling ball of light. Once they reach LA, Pete and Myka interview Larry, a workaholic about to open another in a chain of malls, as well as his ex-wife and their daughter, Callie. Larry's knocking down some mom and pop stores to make way for his mall, so the three go to talk to Wilkie, the most grumpy of the store owners. Any suspicion that Wilkie may have been responsible is erased, however, when the Santa specter shows up and threatens Larry's life.
Not wanting to let him out of their sight, Pete and Myka take Larry to his ex-wife's home for more info. But Claus follows them there, too, and after warning him to be a better man, he starts to make him disappear. Impulsively, Pete grabs Larry's arm, and the ghost loses his power long enough for Myka to incapacitate him with her Tesla. She peels back Claus's mask and reveals him to be a doppelganger of Larry. Attempting to keep Larry safe until they solve the mystery, they take him home and seal off any vents and windows in hopes of keeping the sprite out.
Larry is safe and sound, but when Wilkie shows up with hearty thanks for a letter calling off the demolition - forged by Larry Claus - Larry bursts out of his safe room in a fury. Larry Claus takes this opportunity to complete his earlier job of making Larry disappear, and this time he succeeds. Pete and Myka work together to puzzle out where Larry Claus could've taken Larry Newly.
Claudia's search has gone much better, or so she thinks, when she finds not only the piano, but Artie's long-estranged father. With a massive white lie - that Artie is dying - she persuades Mr. Weisfeldt to return to South Dakota with her. Once there, she uses the same story in reverse to persuade Artie to talk to his father. When the two discover they've been duped, they're furious, but their shared fury turns to bonding, and it's water under the bridge.
On a hunch, Pete and Myka dash to Larry's mall, and find him tied up and disappearing - Larry Claus is going to erase his existence and take his place. The artifact they found - an antique Christmas ornament created during the Christmas armistice of World War I - has been bagged, but to no avail. But when Callie arrives, the evil magic is no match for the pure love she has for her absentee father. She rushes towards him and wraps him in a hug, making the Claus spirit disappear. With the family reunited, Pete and Myka head "home" to their mismatched, happy family.