Somehow, the afterlife as a perpetual, middle school-aged town is a little unexpected. But when eighth grade geek Oliver "Boo" Dalyrymple dies, he finds he's captured in time as he was when he died and housed with all the otherworldly American 13 year olds..
He quickly begins to make friends and get acclimated - turns out in the afterlife you're a slightly better version of yourself, and in this form he easily makes friends - when a new, familiar kid arrives. They were classmates, and Johnny reveals he and Oliver were the victims of a school shooting. Johnny's been in a coma for weeks, but now he's out for information and revenge.
While this isn't a "mystery" book, there is a definite anticipation and anxiety about what the boys may find out, along with some big questions: Who was the shooter? What can they do about it? Would Zig (god) allow a murderer in heaven? Is there a way back home?
I was waiting for a big twist and may have peeked ahead - but it's not a straight-forward reveal and isn't an easy sneak, so be patient and enjoy the unwinding of the story. It's worth the wait.