I have to be honest with you — I don't have any information about a book called *Nineteen Quiet Rooms* by Ottilie Marsh. It doesn't match anything in my knowledge, which suggests it might be very new, very obscure, or possibly a different title or author than you remember.

I'd rather tell you that than make up a twist and have you confidently say something wrong at book club tomorrow!

A few things that might help:

1. **Double-check the details** — Is the title or author possibly slightly different? Sometimes titles get misremembered, or a book might be published under a different name in different countries.

2. **Quick spoiler sources** — Goodreads reviews often contain spoilers (they're usually marked), and Wikipedia sometimes has plot summaries. Searching "[book title] ending explained" often surfaces Reddit threads or blog posts with detailed breakdowns.

3. **The honest book club approach** — You could just tell your group you didn't finish it. Most book clubs are forgiving, and the discussion about *why* you didn't finish can be genuinely interesting.

If you can tell me anything about the book — the plot so far, the characters, roughly when it was published — I might be able to recognize it under a different title. Or if you'd like, I can suggest good questions to ask your book club that let you participate without having read the whole thing!