"There were a lot of adventure books for boys, historical novels by Kenneth Roberts, and whatever mystery novels the alarmed librarian imagined might not corrupt an eager but innocent youth"

This quote is describing the books that were readily available to a young reader in a library. The library had a range of books that would interest a young reader, such as experience books for boys, historical novels by Kenneth Roberts, and mystery novels. The librarian was likely concerned about the material of the secret books, and wished to ensure that they were appropriate for a young reader. The quote recommends that the librarian was careful to choose books that would not corrupt the eager however innocent youth. This quote highlights the importance of libraries in offering access to books that are proper for young readers, and the duty of curators to ensure that the books they supply appropriate for their customers.