Thief of Time. Terry Pratchett.

Man! If you´re reading this, it means that you exist. We, the Auditors, watching you, you register, you are studying. And very soon we will get to you. Immediately after destroy this despicable Discworld, with its elephants, turtles and completely nuts inhabitants. Are you reading this? Then we go to you!

Pleasant impression of the book you are guaranteed, dear reader!