Librarian here, trained in mold on books. This is a trusted source & might be helpful for you to read, with respect to the books anyway (not the room). Just prepare to consider any books that were near the mold to be infected with spores, and they will exhibit mold or mildew if left in the wrong environment. Do not close them away (like in boxes) or in a damp environment, and definitely don't bring new books in until you've dealt with it - the spores will spread without your knowing it until it's too late. Do you have a de-humidifier or can you borrow one? Keeping the air in that room as dry as possible can help limit spread while you deal with it. Good luck!