LAST STOP SUNNYSIDE by Pat Capponi (2006)

Living in a rooming house in Parkdale, Dana Leoni finds herself in the middle of a mystery involving a former housemate whose body has washed up along the Lake Ontario shore where the old Sunnyside Amusement park used to be. When the police decide to close the case, Dana and her remaining housemates--people pushed to the margins of society through mental illness and misfortune--decide to do detective work of their own inspired by their reading of the seedy, but hopeful tales of Janet Evanovich. Their dedication leads them to discover a terrible reality that is all too plausible.