I can’t believe I missed reading Shadows (Nancy Paulsen Books, 2013) by Robin McKinley. I love how the book opens:
“THE STORY STARTS LIKE SOMETHING OUT OF A fairy tale. I hated my stepfather.
It’s usually stepmothers in fairy tales. Well, equal time for step-fathers.”
Teenage Maggie lives in Newworld, where they “don’t have magicians, evil or otherwise.” She lives with her mom, stepdad Val, little brother Ran, and her dog Mongo. She can’t tell anyone about why she dislikes Val., whose from Oldworld Afterall, Newworld is about science and one shouldn’t be afraid of shadows even if they do have extra legs.
I enjoyed the teen speak of Maggie and her friends, the origami folding, and was made nervous by the shadows and other things I’ll let you discover for yourself. It would be one spooky movie! This is my newest favorite book by Robin McKinley.
You can see her other books at her website. My other favorites are Deerskin and Sunshine. 
You can also read Robin’s blog, Days in the Life*,
* with footnotes
here.