Lord Loss - Darren Shan

Grubbs Grady is an average kid. A bit bigger and slyer than a lot of boys his age (he loves to play evil, ingenious tricks on his sister), but nothing special. He leads an ordinary life, and expects it will always be that way. But when his parents and sister behave strangely ... and Grubbs decides to stick his nose in ... his entire world is thrown into chaos. He discovers that demons are real, and that terrible things can happen right in front of your eyes.