The Afterlife Academy — Frank L. Cole

ONE CREEPY BOOK. TWO TWELVE-YEAR-OLD BOYS. A HORDE OF ANGRY DEMONS. WHAT COULD GO WRONG?
 
When Walter Prairie is struck dead by a bolt of lightning, he's fast-tracked through the Afterlife Academy and assigned as a Guardian Agent to protect a High-Level Target. Walter's HLT, Charlie Dewdle, isn't the most popular kid in school. He's a bit paranormally obsessed. And he has just found an old book that could be used to open the Gateway for demons to wreak havoc on earth. Now, it's up to Charlie and Walter to fight an eclectic horde of enemies and protect humankind at all costs. But saving the world isn't so easy. Especially when your protector doesn't know the first thing about the underworld, bullies like Mo Horvath are trying to hunt you down, pretty and popular Melissa Bittner is suddenly talking to you, and your parents think you're going crazy.