Okay so this gets a 3.5 maybe a 4 from me. There is something about writers that can set the whole book in nearly the same place all the way through with out it getting repetitive or boring.
The cave in this book really does it for me. I now have this thing for any books written like this one!! Interesting plot, let's face it better than her other book series.
The aliens have invaded, what, where? That's just my neighbour! This could happen, I like that. It makes you think 'my god damn neighbour could be one of these. Lets go live in a cave/underground cavern'.