It sounds like there might be a slight mix-up with the title or the author, as there is no existing book titled *Nineteen Quiet Rooms* by an author named Ottilie Marsh. 

If you want to double-check the book cover or your book club's reading list and reply with the exact title, author, or a brief summary of the plot you've read so far, I would be happy to help you figure out which book it is and give you the ending spoiler before your meeting tomorrow! 

(For example, if it's a recent mystery/thriller, you might be thinking of something like *The Maid* by Nita Prose, *Eighteen Tiny Deaths*, or *The Madness of Crowds* by Louise Penny, or perhaps a book with a *character* named Ottilie?)