This book is about a boy, who gets taken away to "hell" to help start a warfare against God. The boy doesn't really know what he's doing, but an angel convinces him that it's ok, and will give him whatever he wants. Course the angel is a bad angel.
The boy has a sister, and she meets her guardian angel who shows himself to her, and together with another angel and girl, they go to save her brother and the kingdom of heaven and God. This is a series book, and is the first book in the series.