Disclaimer: When I started reading this book, for some reason, I believed it was the first in the series, so nothing made any sense and it gave me a bad first impression.
Second Disclaimer: It wouldn't have made any difference, because this book has no redeeming qualities and falls into the bloated genre of shallow, thoughtless, pointless Harry Potter wannabes. (And yes, wannabe is a real word. Look it up.)
OK, so here's a quick synopsis: Charlie Benjamin is a magic kid who has no flaws whatsoever and is perfect in every way and battles a Super Rad Awesome Over-Powered Mega-Monster, who's really little more than some cackling crone, named the 5th. He's accompanied by his prepubescent buddies, Theodore, Brooke and Violet, who are equally flawless and perfect in every way. They attend some sort of academy for magic kids, and the adults are all plotting either for them or against them and blah blah blah... Headmaster... blah blah blah... magic sword... blah blah blah... Harry Potter... Together, they all make perfect decisions throughout the book, always being wiser than the adults around them, and defeat the 5th. The End.
In all seriousness, the terms "Mary Sue" and "Gary Stu" have been thrown around a lot in the film and literature worlds lately because of the atrocity that was "The Last Jedi," but if you wanted classic examples of what those terms mean, look no further than these characters. I don't understand why so many authors who write books for young readers don't give their characters any depth, flaws, nuances, or internal conflicts whatsoever. I could understand keeping the themes of their conflicts age-appropriate, but to have none at all is just lazy and bad writing. This story is just one horrible cliche after another. The reason these types of books will never live up to Harry Potter is because Rowling made her characters so much more believable and actually spent time weaving interesting character arcs.
I normally like to put a lot of thought into my reviews, but this book was so utterly freaking boring that I just can't put my normal effort into this.
On the plus side, Brooke does seem to get around a lot and finds some very creative excuses to kiss boys. So there's that.