You're looking for a book that explains Kant entirely? Then you should read Kant's work itself. But then it won't be easy to understand. If you want to have something easy to understand, you'll have to accept it won't be complete. You have to make a compromise somewhere.
You may find this video and the others in the same series interesting: http://youtu.be/kLwiBg4sCaE - of course they oversimplify things.
For more, Roger Scruton wrote a 135-pages introduction to Kant. Also this is not enough to explain everything, but what Scruton does very neatly, besides giving a basic introduction, is showing the modern relevance of Kant's work.
If you're going to read a primary text, I would advise to read an opponent alongside. It always helps to get a better idea of the context and the issues they're dealing with. When I read Kant's Critique of Practical Reason, I read Nietzsche's Also Sprach Zarathustra alongside.