Ellen, a New York lawyer, and her pre-engagement boyfriend Hayden, a politician, are perfect together on paper, but she still has not given him an answer to his proposal of marriage. Ellen and her maternal grandmother Ruth have always had a special bond, going on unusual adventures together, something that Ellen's more conservative mother, Cynthia, has never understood.
The last words Ruth said to Ellen before she passed away was for Ellen to hand deliver a letter for her, it addressed to a Chet Cumberfield in Beacon, Maine, where, as Ellen just learns, Ruth was born and grew up. Chet is someone of whom Ellen and Cynthia had never heard. Ellen has no hesitation in obliging her grandmother's last request. It's a task which she believes will take two days at the most. Upon her return to New York, she plans to give Hayden an answer.
Ellen makes a literal and figurative big splash upon her arrival in Beacon, an event which will forever tie her to a local contractor named Roy in the minds of Beacon residents. Physical evidence of that tie to Roy is something that Ellen wants to erase or hide, especially from Hayden. Ellen's stay in Beacon is extended as she not only has trouble trying to locate the address in question, but she begins to discover more and more information about her grandmother's past about which she previously had no idea.
During Ellen's stay in Beacon, she is guided by the spirit of Ruth, who had a reason beyond delivering the message to Chet for Ellen to go on this journey, all in the name of "returning home for the first time".