Had an excellent book suggested to me by a genius friend called the elegant universe. I have read it... multiple times and LOVED it. I was at london drugs and found IT ON VIDEO YAAAAAH! It help to simplify how physics transformed from newton - gravity - to Einstein, relativity - Quantum Mechanics - string theory - M theory. I find it left alot of very interesting things out of the movie that were in the book, but nevertheless it focused more so and only on M theory. While if you are able to read physics (very well written) if you are wanting a conceptual grasp which explains more the what the bleep, and further down the rabbit hole I would recommend watching the elegant universe.
The book is wonderful it goes into how and why time slows down the faster you go, how it would be possible for worm holes if M theory is correct, and how different dimensions are possible.