In Luke Garner's world, families are only allowed to have two children. To hide him from the Population Police, Luke's parents make him a bedroom in the attic.
During the day, Luke is allowed to go outside to enjoy the fresh air and tend to the animals on the family farm. However, that privilege is soon taken from him. According to the text, Luke's parents must keep him inside after the government forces them to sell the wooded acres behind their home.
When workers begin to build homes on those acres, Luke is forbidden from going outside altogether. To make matters worse, he isn't even allowed to look out the windows. Luke's father is especially harsh in enforcing these rules.
Eventually, Luke must eat his meals on the stairs, away from the family table and the windows. This makes him feel isolated and marginalized. After stressful exchanges with his parents, Luke often heads up to his attic bedroom. There, he looks out on the outside world through the vents on both sides of the roof.
To look out the vents, Luke has to climb up the largest trunks in the attic. What he sees through the vents provides him a context for his family's conversations surrounding the mansions that are being built. When Luke's mother describes their new neighbors as rich city folk called Barons, Luke is able to comprehend her meaning by peering out the vents.
What he sees tells him that his mother is right: the Barons are wealthy and have sophisticated tastes. In particular, the women wear beautiful, form-fitting clothes, while the men are always dressed in suits.
To ease the stress of living a double life (as a member of the Garner family and an invisible member of society), Luke also reads the adventure books his mother brings home. The stories let him pretend that he's a knight coming to the aid of a kidnapped princess or an explorer sailing the high seas in the midst of a terrible storm. Most of all, the books help him forget that he is a third child who must hide in the attic.