It is Christmas time, and all the boys have been invited to Cartman's grandma's house for the holidays. Unfortunately for Stan his parents will not allow him to go. Stan sneaks away and goes with the others.
After a very long car journey, not helped by Cartman and his mom singing irritating songs, they arrive in Nebraska. Kyle then notices an advert for Mr. Hankey appearing at the mall.
The boys soon discover that Cartman's family are a lot like Cartman himself, they are all overweight with voices similar to Cartman, they eat like pigs, and they use all the same catchphrases.
At the Christmas Dinner, Howard Cartman is shown via satellite from prison, and Stan tells everyone that his parents are dead, at least dead to him.
In the night, the boys are seen sleeping in the basement, but were soon woken up by Kyle screaming that he had a nightmare about being in a house full of Cartmans, to which Stan reminds Kyle that they are indeed so. They then hear someone breaking in, and it turns out it is Uncle Howard having escaped from prison with his cell mate, Charlie Manson.
The next day, the boys ask Cartman's family to take them to the mall, but being like Cartman they will not. In the basement, Charlie Manson offers them a ride since he wants some action to which the boys agree.
At the mall, Manson invites Kenny to a more secluded part of the mall. Kyle soon discovers that the Mr. Hankey is a guy in a costume who says there is no real Mr. Hankey. Kyle, driven by anger removes to head of the Mr. Hankey costume revealing the actor inside. The kids there soon riot.
Charlie Manson soon sees another Christmas special based on the Grinch but with Mr. Hankey. Manson finds it a brilliant thing how a nasty person can change to a nice one.
Manson returns with Kenny having had his tattoo changed to a smiley face. The police who have turned up to stop the riot spot Manson and the event leads into a car chase to the Cartmans' house.
Stan's parents soon discover that Stan sneaked away to Cartman's grandma's and follow.
At the Cartman residence, the police threaten Manson and Howard to make them come out. Stan's parents arrive, and he asks the escaping Manson and Howard if he can join them. Manson explains the importance of family and he decides to hand himself into the police. Kenny is also made to show a white flag in surrender, but is gunned down. Manson then apologizes to all the families he tore apart and wants to make himself an example to the world that crime is never an answer.
In the prison, Manson finishes writing another book and turns the light off sadly as he goes to bed. Suddenly the light is turned back on, the Cartman family plus the boys wish Manson a happy Christmas and sing "Hark the Herald Angels Sing".
Right before the episode ends, Stan remarks to Kyle how messed up the entire series of events was (Given the fact that they were singing Christmas carols to a mass murderer).