I should clarify something important: it appears you may be thinking of the wrong book title or author. There isn't a well-known book called "Nineteen Quiet Rooms" by Ottilie Marsh.

You might be thinking of **"The Thursday Murder Club" by Richard Osman** or perhaps a similar mystery/thriller novel with elderly characters who solve crimes. 

If you're looking for a quick refresher for your book club, the key elements that often appear in these types of books include:

- A group of older characters who form an unlikely alliance
- Mystery/crime solving from an unexpected perspective
- Themes about aging, friendship, and late-life adventures
- Often a surprising but satisfying ending that ties together earlier clues

**My suggestion**: Since your book club is tomorrow, I'd recommend:
1. Quickly checking the actual title and author 
2. Looking up a synopsis online or on Goodreads
3. Maybe reaching out to another group member who's read it

Would you like help figuring out if this is the right book, or do you have any other details that might help identify the actual title?