The Cave Between Worlds is a story which reminded me a bit of The Dark Is Rising series. It's about a regular group of children who find themselves caught up in an invisible struggle against supernatural forces. It uses the well-worn but effective concept of Fantastic Racism as its central basis. In this universe, supernaturals are forced to hide and pretend to be human in order to avoid being exterminated by the racist and evil wizards. Whether harmless goblins or dangerous monsters, they are being hunted down because their ancestors served the Dark.
I like the protagonists and their pleasant easy-going manner. There's a scene where they spend time playing Mario Cart and it's a believable enjoyable. None of them particularly stand out as strong personalities but I believed them as teenage boys and that is useful in its own right. I also believed when they befriended the monsters around them. One of my favorite moments of the book was when they asked Malachi a series of outrageously racist (speciest?) questions about being one of the undead.
"Don't vampires kill people anyway?" asked Charlotte. She looked stricken. "Ah. Sorry. That just sort of slipped out. Please don't take it as a suggestion or recommendation."
“Ah, yes,” said David, blithely. “Vampires kill people and drain their blood to feed off of them, don’t they?”
“No, you’ve got that the wrong way around,” said Charlotte. “They drain them first, and then kill them. Their prey have to be alive. At least, in all the vampire stories I’ve heard about.”
“Well, draining them would kill them,” said David. “Obviously.”
“Yes, but the way you put it was that the vampires kill their prey and then drink their blood after they’re dead,” protested Charlotte. “It’s completely different.”
The vampire was watching the argument in bemusement. He cleared his throat. “Excuse me,” he said. “If I may comment, as probably the best expert on actual vampires?”
“Ah. Yes. Sorry,” said Charlotte, flushing.
The world-building is well done with the supernatural justified as races created from magic and given by the Dark, only to betray the Dark in later years. I think it's a bit cheesy that the Dark is behind the racism that is being used by wizards to justify killing the Shadow races. Even so, I think it did an excellent job in wanting us to see the various "monsters" survive and escape from their persecution.
Mind you, if you assume the story is a simple story of specism and genocide then the author will surprise you. There's a lot of twists and turns in the story that I did not expect and appreciated from the author. The protagonists trust a little too easily and while in the real world, too often there are just the persecuted and persecutors, fiction has a higher burden of proof.
Overall, I found the book to be quite enjoyable but I also note that it didn't jump out at me as a storyline either. The villains and their motivations weren't very well-developed beyond simple racism. I've always been fond of the concept of a "Secret World" though and the masquerade is actually justified in this setting. I also felt the author had an easy-going and entertaining sense of humor that made the banter between characters the best part of the book.