As has been noted repeatedly: “To Mock a Mockingbird” by Raymond Smullyan. It’s one of the finest mathematics/logic books ever written for the intelligent layman.
They ship to a very large amount of places for free. My only complaint is that because it is shipping from another country it takes a while to get to you and you don't get any tracking codes from them.
http://www.amazon.com/gp/product/0192801422?ie=UTF8&tag=...
(Yes, that’s an affiliate code. Strip it out and replace with your favourite charity. “Raganwald" is an acceptable answer for “favourite charity.”)