At its core, Summer Island is a novel focused on healing the wounds caused by family secrets and estrangement. At the beginning of the text, Nora is a successful advice columnist who lives in constant fear that her secret—that she abandoned her daughters and is estranged from them—will be revealed to her adoring fans. Notably, these details are not the source of her fall from grace; instead, the public is horrified by her illicit and short-lived affair.

Through Nora, the novel suggests that secrets can have an exhausting and toxic impact. Nora spent most of her childhood and adult life trying to keep things hidden. When she tells Ruby about her father, she explains that she hid his alcohol addiction and his abuse because “[i]t’s what children of alcoholics do. They keep secrets” (210). By masking elements of her life—and the pain they have caused—Nora set into motion a long line of additional secrets. She hid the fact that Rand cheated on her and never revealed her true motivations for abandoning the family, leaving both Caroline and Ruby to assume their mother left to pursue her career. As a result, both Caroline and Ruby live lives engulfed by estrangement and subterfuge: Ruby is unable to get close to anyone, while Caroline struggles in a difficult marriage, unable to disclose her pain.