Literally the only thing I can say positive about this book is that the prose is decent. Other than that, this is atrocious in every regard. There's a lot to complain about here, from the bland characters, to the incredibly slow pacing, to how boring and cliched the fantasy elements are, to the shoddy structure, to the fact that this is ostensibly an adventure story where the adventure doesn't start until two thirds of the way into the novel, to the way Laurie sets up way too many mysteries early on in the novel and fails to address all of them by the end, to the fact that Laurie's interpretation of Greek mythology is so far from the actual myths that this is basically classical in name only. But the absolute worst thing about this novel is Laurie's complete disregard for historical accuracy regarding Morocco, and the racism that results.
Now, I'm no expert on African history, but provided you know how to use Google, you don't have to know a thing about Morocco to know how awful this portrayal is. For example, there are multiple references to a Moroccan government, despite the fact that this book is set in 1937 and Morocco was a French colony at the time. But far worse is the fact that the Jstor and Jichmach tribes featured in the novel appear to be completely fictional. They might be based on real Moroccan tribes - like I said, I'm no expert on African history - but somehow, I doubt it. The tribes have no real culture to speak of - their only characteristic seems to be that they're at war with each other. This resulted in some pretty bad racism, where only a couple of the African characters are sufficiently humanized - most of them are portrayed as savage warriors, whose only motive is tribal wars. Even when Laurie does humanize an African character, she undermines that humanization - when Ian interacts with Jifaar, he remarks that he didn't expect Jifaar to be so "civilized". Accurate to how a European interacting with an African would think? Yes. But when you consider that this book is written for kids roughly 7-12, who are very impressionable and probably know nothing about Africa except for stereotypical portrayals... yeah, it's a dangerously bad writing decision.
Like I said, this book has a lot of other problems, and I don't recommend it to anyone. But I haven't seen anybody else discuss this book's awful, awful portrayal of Morocco, and I wanted to let any prospective readers know about the problem before they pick this book up. Don't worry - if you decide not to read the book for that reason alone, you're not missing anything.