The Book of Ruth is about two sisters, Ruth Matilda Clarkson and Cora Undine Lasciter, who survive the trials of a challenging childhood and a demanding father in 1940s America and then find themselves swept up in the powerful currents of the men who come into their lives.

Ruth, the older, whose life is a sort of modern-day parody of her namesake, Ruth the Moabite of the Old Testament, marries a young man she meets at college, the enigmatic Richard Clarkson, a man controlled by his appetites and unending desires, and leaves her family in St. Louis and moves to the rural town of Ox Bend, Missouri, where she becomes part of the Clarksons' family-run funeral business. After they have been married only a few months, Ruth's family, attempting to avoid a scandal, asks her to adopt her sister's illegitimate child, Aaron, who turns out to be a special-needs child who ultimately transforms Ruth's life in ways she never thought possible, even after his death in 1990.

Her estranged sister, Cora Lasciter, a beautiful, impetuous, free-spirited woman and a survivor of sexual abuse, gives birth to a child, Aaron, at age seventeen, signs over her parental rights to her sister, and then moves from relationship to relationship as she struggles with the demons from her past. Years later, when she attends Aaron's funeral, the two sisters, bound by their connection to the child, gradually rebuild their filial connection, and together they face the pains of infidelity, the loss of love, and the vicissitudes of old age.

It's an uplifting survival story of two very different women connected by the unbreakable bond of sisterly love, unending faith, and the innocent truth and unfiltered love of a child who brings them back together, and represents the possibility of love, forgiveness, and ultimate redemption.