Petruso is a freelance writer and editor, with an undergraduate degree in history and Master's degree in screenwriting. In this essay, Petruso considers how the idea of insider versus outsider manifests in the characters of the novel, as well as the dynamics of their neighborhoods.

In Mystic River, a palpable tension exists between insiders and outsiders—people who belong and people who do not. Although the events in the novel blur the distinction between insider and outsider, the tension between these two conditions plays as important a role in the plot as it does in the daily lives of the novel's characters. The communal characteristics of the Flats neighborhood create opportunities for safety, victimization, criminalization, and absolution, and thus, this theme drives the action of the story.

Nearly all the residents of the Flats have spent their entire lives in the neighborhood, with the exception of a...