Rosalind, Skye, Jane and Batty are the Penderwick sisters. One summer, Rosalind goes to New Jersey and Sky, Jane and Batty go to Point Mouette, in Maine, with their aunt. The OAP, or Oldest Available Penderwick, usually Rosalind, is now Skye. Skye is not sure she will be able to do it. And when they arrive, Skye loses her carefully written list and is worried that Batty will be hurt!
The Penderwicks at Point Moutte is good for a large age range. One of my favorite parts was when Skye got mad at Jane for reasons I can't tell. It was my favorite of the three Penderwick books.