"Christmas Carol" isn't so much a Christmas episode as it is regular ol' X-Files episode set during Christmas time. That's a little disappointing considering I wanted some Christmas cheer with my sci-fi; it's also frustrating that "Christmas Carol" starts a new arc in the series with a two-part episode leading into the next one, "Emily". Still, there are worse ways to spend the holidays than with Dana Scully, who gets some leave from the FBI to visit with her family for Christmas.
Mulder is absent from this episode except for a quick scene where Scully contemplates giving him a call; it's been a while since I've seen any X-Files, but with the episodes I have seen, it's out of the ordinary for the two to be separated for an entire episode. Normally the idea is for the two to play off of each other, so it's interesting to see Scully working alone on a case she gets sucked into after getting a phone call from a mysterious woman who sounds just like her sister.
Scully investigates where the call came from, only to find that she's traipsing through a suicide crime scene - no call could have come from the house she traced the spooky call from, because the police had been there for that amount of time and no one had picked up the phone. Is it a call from the grave? Something weird from Scully's sister?
To make matters worse, there's a little girl wrapped up in the proceedings who looks just like Scully's sister when she was younger. It gets Scully wondering - could this be her sister's daughter? Blood tests are pulled, and the results come back negative.
"Christmas Carol" uses the holiday season for very little; however, it's mainly a method to get Scully back home with her family, and to see the intricacies of their relationships. These aren't really the strong points of the episode, and Scully's brother and mother are mostly absent except for a few key exchanges. But the real focus of "Christmas Carol" is on Scully's wish for a child. She's been left barren after a kidnapping/assault, and now that her brother's wife is pregnant with child, she finds a yearning inside of her for something that no one can give her for Christmas.
The twist at the end of "Christmas Carol" is definitely built up to work; it makes sense that the identity of the child would turn out to be Scully's own daughter. The blood tests match, but Scully's not sure how it could have happened. The X-Files proves with this episode that it doesn't need both of the partners to work; yet there is something missing during the investigations, and there's no one to alleviate Scully's paranoia throughout. No wonder Mulder is always around.
I wouldn't recommend "Christmas Carol" for festive viewing simply because the Christmas aspect of the episode isn't prevalent. It's barely there at all, actually, and unless you're planning on continuing through season 5 of The X-Files, it's best not to get wrapped up in the continuing plot.