With autumn already in full swing, the Peanuts gang prepares for Halloween. Linus van Pelt writes his annual letter to The Great Pumpkin, despite Charlie Brown’s disbelief, Snoopy’s laughter, Patty’s assurance that the Great Pumpkin is a fake, and even his own sister Lucy’s violent threat to make her brother stop. When Linus goes out to mail the letter but cannot reach the mailbox, Lucy refuses to help him; so he uses his blanket to open the box, and throws in the letter.
On Halloween night, the gang (including Charlie Brown’s younger sister Sally) goes trick-or-treating. On the way, they stop at the pumpkin patch to ridicule Linus’ missing the festivities, just as he did last year. Undeterred, Linus is convinced that the Great Pumpkin will come, and even persuades Sally to remain with him to wait.
During trick-or-treating, the kids receive assorted candy, apples, gum, cookies, money, and popcorn balls — except for Charlie Brown, who for some reason is given a rock from every house they visit, possibly due to the ridiculous amount of holes in his ghost costume.
After trick-or-treating and another visit to the pumpkin patch, the gang goes to Violet’s Halloween party. Meanwhile, Snoopy, wearing his World War I flying ace costume, climbs aboard his doghouse (imagining it to be a Sopwith Camel fighter plane) to fight with the Red Baron. After a fierce but losing battle, Snoopy makes his way across “the countryside” to briefly crash the Halloween party, where he is entertained by Schroeder’s playing of World War I tunes on his piano, and then goes to the pumpkin patch. When Linus sees a shadowy figure rising from the moonlit patch, he assumes the Great Pumpkin has arrived, and faints. When Sally sees that it is only Snoopy, she lectures Linus for making her miss the trick-or-treating activities as well as the Halloween party festivities as the kids come to take her away with them. As they leave, and still convinced that the Great Pumpkin will materialize, Linus promises to put in a good word for them.
At 4:00 AM the next morning (November 1st), Lucy realizes that Linus is not in his bed. She finds her brother asleep in the pumpkin patch, shivering. She brings him home, takes off his shoes, and puts him to bed. Later, Charlie Brown and Linus are leaning against a wall, commiserating about the previous night’s disappointments. Charlie Brown attempts to console his friend, admitting that he himself has done stupid things in his life also; this only infuriates Linus, who sets off on an angry rant vowing that the Great Pumpkin will come to the pumpkin patch next year, as Charlie Brown listens with a visibly annoyed look on his face and the credits roll.