The Legend of Spud Murphy is part of a series called "Eoin Colfer's legend of ...", written by the Irish author Eoin Colfer, author of the best-selling series Artemis Fowl.
In their summer holidays their mother decides that they should take up an educative hobby, so she sends them to the library twice a week.
Without being seen, Marty sneaks to the adult section and takes a book while the librarian is absent.
Will and Marty read "Spies in Siberia" together until Spud comes along and takes a look at the adult section.
Mrs Murphy is happy they left the carpet to find a book, and not because they wanted to mess up the library.