Alex has always known her best friend and next-door neighbor, Will, will be there for her. That's just how it's always been. Until a girl from the pool named Rebekah comes over to them and says hi. Suddenly, Will is changing his clothes, restyling his hair, and breaking all their summer plans and Alex is not happy about it.

Every summer, she and Will come up with a new challenge. This year, it's a treehouse. Now Alex is wrangling up summer jobs and keeping tabs on the new girl, hoping that in completing their treehouse, she can keep from losing her best friend and her summer from falling apart.