I want to know the worth of an old book.?

I have a copy of Sir Arthur Conan Doyle's "His Last Bow". It was copyrighted in 1917, but I can't find the edition of it anywhere on or in the book. I want to find out how much its worth, if its worth anything at all. Can someone tell where I can find sites where I would be able to find out on my own, or if anyone knows how much it could possibly be.