Diary takes the form of a "coma diary" telling the story of Misty Marie Wilmot as her husband lies senseless in a hospital after a suicide attempt. Once she was an art student dreaming of creativity and freedom, but now, after marrying her husband Peter while they were both still at school and then giving birth to their daughter shortly after, she is eventually brought back to Waytansea Island, a place that was once-quaint but is now tourist-overrun. Misty has been reduced to the lowly condition of a mere waitress within a common resort hotel. Peter, before falling into his coma, was building hidden rooms within the houses he was remodeling and scrawling vile messages all over the walls; this is an old habit of builders but it's been dramatically overdone in Peter's case. Angry homeowners are suing Misty left and right and her dreams of artistic greatness have been ruined. But then, as if she was possessed by the spirit of the fabled Waytansea artist Maura Kincaid, Misty begins painting again, excessively and compulsively.