Mistreated by his father, and missing his only friend Sunny, Bobby takes off on a road trip with Val Reed and her daughter Rosa in a recently de-commissioned bookmobile. Val had been charged with the weekly cleaning of the Mobile Library and allowed Bobby and Rosa to come with her while she worked so they could read books (and take some home, as long as they brought them back). As she works, Val explains to the children that not all mobile libraries are trucks; in some parts of the world they use animals. In Kenya they use camels and in Zimbabwe they have a library cart pulled by a donkey and in Thailand they use elephants. Val also explains that in Norway they have a library boat that "can take the books to all of the old people who live on little islands" (see my post on Swamplandia! for a fun library boat read) and more about book mobiles can be found here.
Val makes clear to Bobby that she is not the librarian, although she wishes she were. She does tell a gas station clerk that she is the librarian when he questions her about driving the big truck "I wouldn't make much of a truck driver with these little, feminine arms, now would I?" she offers by way of explanation. Neither is she afraid to shush like a pro those who say inappropriate things.
When Val learns that the mobile library service has been stopped "because it costs too much money" the she decides to take the children off on an adventure, disguising the truck with some stolen paint. Val's biggest concern with the closing of the mobile library was the loss of "the stories...[and] discoveries they had made in them...they had cheered a victorious hero and willed a villain's comeuppance...Parts of themselves they'd never noticed absent, concealed in the ink on the page". Bobby likewise had pangs of missing the library even before it closed.
Despite the many ways his imagination had been opened up by the mobile library, he could not imagine wanting to be anywhere else, with anyone else. The mere thought of it filled his bones with the inexorable ache of yearning.In addition to missing his friend Sunny Bobby is also missing his mother, who left the family some time before. Bobby had been collecting pieces of his mother's clothing, hair, and other relics so that when she returned they would be able recreate everything just as it had been. Bobby considered himself his mother's archivist, and kept his files hidden under his bed. They are the only thing he takes with him from home when he starts on his grand adventure.
There are a lot of references to other works (mostly children's books) both subtle and overt in this one.