I received an advanced reader's copy and some of the beginning chapter transitions and some backstory were clunky. Perhaps it will appear differently in the final copy. Once the action kicks into high gear and the plot sticks mainly with Tod then I was hooked. I would have preferred less Septimus Heap characters. I thought they were a distraction to Tod's storyline. I also think that readers will enjoy it most if they are familiar with the Septimus Heap series. It is confusing otherwise because Sage mentions many past incidents that happened to characters but doesn't explain them all. If she did it would slow the plot down even more which is why I think there should have been less.
The author creates tension by having the characters disagree with each other even if it contradicts the character's traits. Sometimes Oskar would be level-headed and other times impulsive. Sometimes the adults believed the kids and other times they didn't even though their past history would suggest otherwise. I found the pattern tiring, but then I read the book in one sitting and most readers won't do that. (I was stuck on an airplane for for 10 hours.) A light entertaining read.