The Naughty Books - The trilogy

Elspeth is a unique librarian guarding an arcane library's restricted section, which contains spell books that offer temporary transformations and fantasies. When she uncovers a hidden room with permanent, irreversible books, she faces unforeseen consequences, including the transformation of her colleagues and the arrival of powerful, insatiable demons. As chaos ensues, Elspeth must navigate the fallout while confronting her own secret desires, in a story designed for mature readers.