Cassie, competitive swimmer and rising seventh grader, plans to spend her summer at the pool with her friends. That way she won't be stuck at home with her sister and her sister's baby.

Julia used to be the perfect big sister: she played great games and took good care of Cassie. Now life at home revolves around Julia and her daughter, Addie. No one pays much attention to Cassie--not to her swimming, and not to what's gone wrong with her friends.

When Julia confides in Cassie that she'll be leaving with Addie--without telling their parents--Cassie jumps in the car, too. As the days of lumberjack breakfasts and hotel pools start to add up, Cassie has to wonder: Could the sister who seems to be the source of all her problems also be the friend she's missed the most?