AJ is a buttoned-up, responsible student attending a high-achieving high school in Michigan. She lives with her mother, stepfather, and two younger half sisters.

Della spends every summer with her father in Florida. A free-spirited wild child, she spends as much time as possible on the beach with her friends and older siblings.

But there's a catch: AJ and Della are the same person. Adelaide Beloise Jepsen to be exact, and she does everything she can to keep her school and summer lives separate.

When her middle sister crashes her carefree summer getaway, Adelaide's plans fall apart. In order to help her sister, save her unexpected friendship with a guy who might just be perfect for her, and discover the truth about her own past, Adelaide will have to reconcile the two sides of herself...and face the fact that it's perfectly okay not to be perfect all the time.