Littleport, Maine, has always felt like two separate towns: an ideal vacation enclave for the wealthy, whose summer homes line the coastline; and a simple harbor community for the year-round residents whose livelihoods rely on service to the visitors. Typically, fierce friendships never develop between a local and a summer girl--but that's just what happens with visitor Sadie Loman and Littleport resident Avery Greer. Each summer for almost a decade,...