A delivery truck parks directly in front of the fort's only exit, leaving the kids stranded just as trick-or-treating is about to begin.
The Belcher children—Tina, Gene, and Louise—along with their friends Darryl and the Pesto twins, spend Halloween night trapped in their elaborate cardboard fort in the alley.
The title is a clever play on the word "fortnight" (meaning two weeks) and the cardboard fort that serves as the episode's central setting. It is widely considered one of the best holiday specials in the series.
Bob and Linda spend the night struggling to finish the kids' massive "dragon" costume, eventually deciding to go trick-or-treating in it themselves when the kids don't show up.