I love book stumpers. It's fun in the library, and it's fun in the web, whether it's a stumper on a listserv such as child-lit or yalsa-bk or What Was That Book on Live Journal or checking out the Loganberry site.
Usually, the book is a children's book or a teen book. I'm also amazed at how many times the description is for The Girl Who Owned A City, The City Underground, or From The Mixed Up Files of Mrs Basil E Frankweiler.
I've had some stumpers that I've solved from work; reading old reviews and "best of" lists from the 1980s and 1970s. There is a joy in finding that old love.
Here's my current Unsolved Book Mystery; does it sound familiar to anyone? I cannot remember when I read it; so assume it was published no later than 1988. Also assume, as is the nature of memory, that I've remembered some details very, very wrong.
Some type of summer camp in the mountains, and I think the camp was located somewhere in or near India. One of the campers was very peace, love, & brotherhood ish and while he wasn't some active preacher-type, the other campers started to follow him (very Jesus like). The parents were worried about their children so forcibly invaded the camp; the narrator, who was Judas-like (main character's best friend and possibly person who told the parents the location of all the kids), ends the story of wanting to get back with the group and sometimes walks along the street, looks at someone, and knows from the look in their eye they are part of this movement.
If you have an unsolved book mystery, let us know & we'll see if we can figure it out.