When Henry Bigg's parents are lost in Africa, the boy must go live with his mean Uncle Augustus. Tom and Lucy Little fall into Henry's suitcase and end up in the unfamiliar and frightening world of Augustus. While hiding in the walls, the kids discover Augustus wants to be Henry's guardian so he can tear down Henry's house and build a shopping center on the land to make him rich. As the Littles live in the walls of Henry's house, and the bulldozers will be there soon, Tom and Lucy are frantic to get home. They reveal themselves to Henry, who is astonished to learn of their existence, but glad to have new friends, particularly in this unhappy household.