You need to login to do this. Beginning with Season 18, the show follows at least one continuous storyline throughout each season. The Spirit of Christmas: The two Christmas shorts that South Park spawned from.
Trailer / Preview:
Cartman Gets an Anal Probe”: Alien visitors are coming to town after Cartman tells Stan and Kyle about his dream of being abducted and a string of cow mutilations are being investigated by Officer Barbrady.