James Archer is a biracial fifteen-year-old who has just been relocated to a new foster home after leaving his former placement. He is being fostered by the family of Lulu, his biological half-sister, older by one year, who was adopted as an infant. Her adoptive parents never knew of James's existence until recently, when he was removed from his previous placement, a social worker found them, and she reached out to them about fostering him.

Lulu attempts to establish a relationship with this brother she's just met as James unpacks his backpack, which holds everything he owns in the world. James is resentful of Lulu, who has grown up with loving parents in a comfortable home. But as he unpacks, he begins to tell Lulu about his past. The story of his life is told in flashbacks inspired by the various objects in his backpack.

James's memories start in early childhood and proceed to the present. Ultimately, the story reveals the events that led to James's removal from his most recent placement. The last chapter has James and Lulu sitting in his room, fully unpacked, acknowledging all the differences in their lives up to this point. They are united as siblings, hopeful about their future as a family.