Does it count as reading an adult book when the writer is clearly more used to targeting 8-year-olds? Creepy twins, seriously idiotic lead female ("oh, there's a major hurricane coming straight for the island I want to write about? HANG ON I'M GOING THERE ANYWAY, IN THE PATH OF THE STORM"), and a plot that feels derivative of something I can't put my finger on--The Shining (but not quite), everything by Stephen King ever (but not quite). Another review mentions the movie Orphan, which I didn't see, but I can see the comparison. 
 And I didn't hate this. Sure, I cringed at the writing and found the Big Reveal a little underwhelming (I didn't actually call the ending, mostly because I sort of just assumed and wasn't surprised by it). But it was engrossing and a quick read and kinda fun on those grounds. But not one I'm going to suggest everyone run out and read.