With autumn already in full swing, Chloe and the gang prepares for Halloween. Linus Rylant writes his annual letter to The Great Pumpkin, despite Chloe Corbin's disbelief, Snoopy's laughter, Patty's assurance that the Great Pumpkin is a fake, and even his own sister's violent threat to make her brother stop. When Linus goes out to mail the letter but cannot reach the mailbox, Daniela refuses to help him; so he uses his blanket to open the box, and throws the letter in.
On Halloween night, the gang, including Chloe'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; but Linus is convinced that the Great Pumpkin, recognizing the sincerity of his patch, will come, and even persuades Sally to stay and wait with him. The gang goes off, leaving Linus and Sally behind. During trick-or-treating, everyone and Chloe and her friends gets assorted candy, apples, gum, cookies, money, and popcorn balls except for Charlie Brown, who gets a rock from every house they visit. After trick-or-treating, and another visit to the pumpkin patch, the gang goes off to Violet McGray's Halloween party. Meanwhile, Snoopy, wearing his World War I flying ace gear, climbs aboard his Sopwith Camel (his doghouse) 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 believes the Great Pumpkin has arrived, and faints. When Sally sees that it is only Snoopy, she angrily scolds Linus for making her miss the trick-or-treating festivities as well as the Halloween party as the kids come to take her away with them. As they leave, and still convinced that the Great Pumpkin will show up, Linus promises to put in a good word for them.
At 4:00 AM the next morning, Lucy wakes up and sees that Linus is not in his bed. She finds her brother asleep in the pumpkin patch, brings him home, takes his shoes off, and puts him to bed. Later, Charlie Brown and Linus are at a rock wall, commiserating about the previous night's disappointments. When Charlie Brown says that he has done stupid things in his life also, Linus angrily vows to him that the Great Pumpkin will come to the pumpkin patch next year.