This is a Christian based series of books for children who are between the ages of nine and twelve years old, maybe thirteen.There are interesting story lines in the series that deal with the death of a parent or loss of a parent; the feelings of pre-teen children who are caught in trying to understand their own feelings about loss and the world around them. Their mother remarried; and has introduced them to God/church, so there are mixed emotions about this:right and wrong, telling the truth to a parent and vice versa. There is quite a bit of dialogue between brother and sister, who support each other, and share what to do in solving the current mystery. There is a means for how a step-parent may interact with his step-children. Their mother and step-father (who also has a teenage daughter) have their own secrets to deal with and how much they think they should tell the twins and younger brother about their deceased father; how do they become a real family. The twins are quick to pick-up on clues about adults and classmates. There are also situations about bullying; parent rules to follow; and mysteries to solve around what happens at school. I think the series is a good read for children who enjoy mysteries and the authors actually have "serious thinking" children, which in wonderful, it's real. I highly recommend these books for boys.