Henry is a loner. He's had enough of people and decides one day to leave them all for good. He goes out into the forest and builds himself a fort made out of cardboard and shower curtains. He fills it with old toys and books and enough food to last him months without seeing anyone. Then Wendy comes along. Wendy is alone and she would prefer not to be. She stumbles across Henry's fort and decides she wants to be a part of what he's doing. Despite his initial resistance, the two begin to navigate a new world of solitude together.