The opening credits show a winter snowfall and Charlie Brown gets his sleigh out of storage, only for the sleigh to roll downhill and hit a pile of snow, causing Charlie to give his usual remark of "Good grief!"
Charlie Brown is then pretending to be a musher with Snoopy, but Snoopy refuses to pull the sled. Charlie Brown angrily remarks that dogs in the Arctic are workers, not pampered pets. Charlie Brown decides to demonstrate how to run, while Snoopy rides. Snoopy takes advantage of this to make Charlie Brown pull the sled! When they arrive back home, Charlie Brown is too tired to play anymore, so Snoopy goes inside. He makes himself a fancy dinner with five pizzas and milkshakes. Charlie Brown comes in and tells Snoopy that Arctic dogs are only fed once a day, and that their meals largely consist of cold meat and raw fish (to which Snoopy blanches and gives a look of "it is too bad to be them"). Charlie Brown comes to the conclusion that Snoopy is "an overly civilized" dog, and remarks he sure hopes Snoopy can handle that overeating, as undigested food often causes nightmares.
After dinner, Snoopy goes on top of his doghouse, and falls asleep. While he is sleeping, the scene around him changes to an image of the Arctic. Snoopy wakes up to an owner of a pack of Arctic sled dogs whipping him. The owner makes him join the other dogs, and makes them all run and pull him on his sled for a while. When they come to a resting point, the owner throws them raw meat, all the dogs eat some, but when Snoopy goes near the meat, they bark at him to show him he is not allowed to have any. The dogs also take turns barking loudly at Snoopy in order to let him know he is indeed an outsider. That night, when Snoopy is cold, he tries to huddle with the other dogs for warmth, but they refuse to let him do that, too. Snoopy eventually builds himself a doghouse out of snow and sleeps on that instead.
The next day, Snoopy is treated no better. He is continually mistreated by the owner and other dogs. They deny him any food or water and he is forced to run all day. At one resting point, Snoopy becomes so hungry that he sneaks into a honky-tonk. Inside, he steals a sandwich and a mug of root beer. He then finds some coins, and uses them to play poker. While playing poker, Snoopy keeps a very straight face and beats everyone by having the improbable five aces. Snoopy's win causes a brawl, making Snoopy escape into another room to hide.
In the next room, which has a backdrop of Paris painted on it, Snoopy finds himself on stage with a spotlight on himself. He does a softshoe dance to a song that plays, and is applauded. However, when the next song is more lively, Snoopy impersonates a can-can dancer, causing the audience to boo at him and start throwing food at him. Snoopy is thrown out of the bar and finds himself back with the sled dogs, and forced to run again. Snoopy is continuously seen running and being denied food and water.
That night, Snoopy decides he can not take it anymore by being harassed by the other sled dogs. He can hardly walk due to all the running he has done and the lack of food or water. He breaks down in tears and clearly wants to go home. He becomes so fed up, that he decides to do something about it. He bares his fangs, falls to walking on all fours and challenges the Alpha Male of the sled dog pack to a fight. Snoopy beats him and becomes the new alpha male of the pack. He decides to take revenge on the other dogs. He barks at them very loudly denying them any food or water.
As Snoopy is leading the dogs around, he accidentally leads his owner and the other dogs over an ice-covered lake. The ice cracks and causes all the sled dogs and the owner to be swallowed into the water. Snoopy is being pulled into the lake, but grabs onto the side begging for his life. The scene then changes to his own doghouse, with Snoopy holding onto his doghouse, then collapsing, causing him to awaken. He is relieved that it was all just a dream.
Snoopy runs into the house and Charlie Brown answers the door. Snoopy acts out his dream in pantomime, Charlie Brown looks at him like he is crazy for a moment, before letting him come inside for the rest of the night, saying, "Boy, that must've been some nightmare". Snoopy then makes himself an ice cream sundae. Afterwards, he goes to bed next to Charlie Brown. Charlie Brown opens his eyes in dismay, then falls asleep.
- This special is unusual in that Snoopy and Charlie Brown are the only members of the Peanuts cast to appear in it. (The only other Peanuts special in which no child Peanuts characters apart from Charlie Brown appear is It's the Girl in the Red Truck, Charlie Brown.) There is also very little dialogue in What a Nightmare, Charlie Brown because only Charlie Brown's speech is intelligible.
- The plot is similar to that of Jack London's Call of the Wild.
- This was the first special Bill Melendez directed since 1973's A Charlie Brown Thanksgiving.
- The owner of the Arctic dogs is shown only in shadow, and talks in a much deeper "waa-waa-waa" voice than is usual for adults in the Peanuts TV specials.
- Snoopy makes only two pizzas, but when he returns to the oven there are four visible. When he puts them on a pile, there are six, but while he is being scolded by Charlie Brown there are only five.
- Snoopy puts chocolate syrup on his ice cream sundae even though chocolate makes dogs sick.
- After Snoopy howls like a wolf, the sled dog on the second left turned from orange to baise while snarling, but after they slept, the dog on the second left turned back orange, but turned baise again while Snoopy was trying to stay warm by sleeping next to the sled dog.
- What a Nightmare, Charlie Brown on the Internet Movie Database.
- What a Nightmare, Charlie Brown on the Big Cartoon Database.
- What a Nightmare, Charlie Brown on AllMovie.
- What A Nightmare Charlie Brown on TV Tropes.