Trapped opens an unspecified amount of time after the completion of the story’s events. Scotty Weems (nicknamed Weems) introduces himself as the narrator and details the severity of the nor’easter (a type of snowstorm specific to the New England region) around which the book centers. Chapter 2 returns to the day the storm began, and events work their way forward.

Due to the storm, school will let out early. Weems is upset because his basketball game will no longer take place, and he put in extra hours of practice off-season. Jason, one of Weems’s best friends, asks Weems and Pete (another friend) to stay after school to work on his shop project. Having nothing else to do, Weems and Pete agree. A few hours later, the boys regret their decision. Along with four other kids (Les, Krista, Julie, and Elijah), the seven become the last group of kids waiting for rides home. By nightfall, the kids are still at school and the power has gone out. With no heat or light, they settle down for the night, figuring the snow will stop so they can go home the next day.

When Weems wakes in the morning, he finds eight feet of snow fell overnight and more still falling. The seven prepare to wait out the storm, breaking into the cafeteria to get food. They move into a classroom on the second floor and split into groups (Weems and his friends, Krista and Julie, Les and Elijah).

Days pass, and the snow doesn’t stop. When the temperature in the building drops and the pipes freeze, the kids must build a fire for warmth and defrost snow to drink. Little by little, the subgroups break apart as the kids realize they need to stick together. They continue to take what they need for supplies from the cafeteria, main office, and nurse’s office. Jason works on converting his shop project into a makeshift snowmobile, and Weems makes snowshoes out of a need to keep busy.

When part of the roof collapses beneath the weight of the snow, waiting for help isn’t an option anymore. Pete takes Jason’s project into the storm, intending to find help. While he’s still in sight of the school, the snowmobile flips over, burying Pete in the snow. Weems uses his snowshoes to go rescue Pete but finds his friend dead. Having gotten this far, Weems continues, knowing he’s the only hope for the group. Hours later, Weems passes out from exhaustion and hypothermia. The National Guard flies overhead in time to save him, and Weems tells them about his trapped friends. The story closes with the National Guard heading back toward the school.