The Book of Ruth is the debut novel by celebrated writer Jane Hamilton. Ruth is a small town girl who grew up in the shadow of a controlling mother. Ruth's little brother is highly intelligent and she often falls in comparison, causing her to grow up searching for someone who can see past her shortcomings and love what is left. Ruth finds this in Ruby Dahl. It does not matter to Ruth that Ruby will not get a job, that Ruby spends all his money on beer and drugs, or that he cannot get along with her mother, May. All Ruth can see is that Ruby loves her and that is enough, until the day it is not. The Book of Ruth is a poignant, heartbreaking story of one woman's attempt to understand the tragedies of life and how her simple desire to be loved leads to the loneliest place a person can experience.

Ruth looks back on her life and the one consistent thing there is her mother May. Ruth begins her story with May's, telling how May was the oldest of eight children, forced to take on the bulk of the chores from the time she was old enough to see over the kitchen counter. May lost a brother at a young age which left her with a dark sense of humor, a sense of humor that would often see her threatening suicide in the presence of her younger sisters. All this seemed to change when May met Willard Jenson. Willard was a good looking, gentle man who swept May off her feet; however, May's happiness would not last long. Willard was drafted into the war and died in the Pacific. May eventually married again, to Elmer Grey. With Elmer May had two children, Ruth and Matthew. However, this marriage was doomed to failure as well, with Elmer leaving the family to pick grapefruit in Texas.

From an early age, Ruth can remember May comparing her to Matthew, her younger brother. Matthew was always smart, doing everything faster than Ruth, making good grades and learning complicated math formulas that May could never hope to understand. Ruth remembers torturing Matthew, ruining his belongings and throwing things at him. Ruth despises Matthew because he is the center of May's world. May is cruel to her daughter in other ways as well. When Ruth helps deliver a baby sheep on her own, she asks May about how babies are made. May laughs the question off, telling her daughter confusing things about how people do what animals do, but they like it. Ruth is confused by this, unable to understand how anyone could enjoy such a thing.

Ruth struggles in school and is often placed in the lower academic classes. In elementary school, Ruth is told by a teacher to write a letter to someone. Almost everyone in the class chooses a classmate, but Ruth has no friends in her class. Ruth begins to write to her Aunt Sid, May's youngest sister. Ruth met Sid only once, even though she only lives forty miles away, because May had a falling out with Sid over the contents of their parents' home after their deaths. Sid responds favorably to Ruth's letters, encouraging her to write more. Soon Ruth finds herself writing Sid crazy stories, making her life sound infinitely better than it really is. This pen pal relationship will last throughout Ruth's childhood and into adulthood.

In high school, Ruth begins working for Miss Finch. Miss Finch is blind, so Ruth sets up books on tape for her to listen to in the afternoons. At first Ruth is uncomfortable around Miss Finch and does not want to stay, but she becomes so involved in the books that she begins to look forward to sitting with Miss Finch. Sometimes Miss Finch does not want to listen to books but to talk. Miss Finch tells Ruth all about her marriage and the trips she made with her husband. Ruth shares her letters from Aunt Sid with Miss Finch. They become close friends, sharing their stories as well as the stories of Charles Dickens and Jane Austen.

Miss Finch becomes senile about the time Ruth graduates high school. As Matthew goes off to a new life at MIT, Ruth goes to work at the dry cleaners as a finisher alongside her mother, May. During this time Ruth becomes good friends with Daisy Foote, the daughter of her mother's closest friend. It is Daisy who takes Ruth out to the lake one night and introduces her to Ruby Dahl. Ruth is mesmerized by Ruby's good looks and his ability to seem so completely relaxed. When Ruby shows up at the dry cleaners and asks her out, Ruth jumps at the opportunity. It is an awkward date at first, but slowly they both relax with the help of alcohol. It is a beautiful night, until Ruby takes Ruth to the local make out spot and forces himself on her. Ruth is traumatized by what he has done, but Ruby is the only man to ever show an interest in her, so she accepts his apology and continues to see him.

Ruby and Ruth date for only a few months before they get engaged. They have no plan for the future, no means to move into a home of their own, but they go ahead with wedding plans just the same. Ruby moves in May's house with Ruby after the wedding. It seems an ideal situation at the beginning, a way for Ruby and Ruth to save up for a home of their own while also helping May stay in the home she has lived in for nearly twenty years' however, things begin to go downhill almost immediately. May dislikes Ruby and thinks Ruby is lazy because he will not get a job and works on mediocre birdhouses all day long. Ruth does not mind Ruby's lack of gainful employment, however, and often finds herself playing mediator between her mother and husband.

After six months of marriage, Ruth finds herself pregnant. At first May is upset, but with time she becomes excited at the thought of having a new life in her home. The pregnancy seems to bring the family together, giving them a united goal to work toward. After the baby, Justin, is born, this unity continues for a few months. The first few months are heaven to Ruth who has been able to stay home with both her baby and her husband; however, the bills must be paid and Ruth must go back to work. Artie, their boss at the dry cleaners, works out a schedule where May, Ruth, and Ruby can work part time, but one will always be home with the baby.

May is a wonderful grandmother, but from the very beginning she takes over the role of parent to such a degree that she often will not allow Ruby to take his own child for a ride in the car or to play with him in the style that he prefers. May sets rules, including not allowing the baby to eat sweets, with which Ruby and Ruth do not always agree. However, it is May's house and they need her help babysitting Justin. They have little choice but to follow May's rules, but the tension continues to build between her and Ruby.

When Justin is nearly three, Ruby and Ruth learn of an apartment they can rent cheaply. At the same time, Ruth learns that she is pregnant again. Ruby and Ruth tell May their wonderful news, but May is not happy. May knows that without Ruth's paycheck she will never be able to stay in the house alone. They argue, but Ruth's mind is made up and May backs down. Then one Sunday a few weeks before the big move, the family sets down to dinner together after a lovely day spent at church. In the middle of the meal, Justin asks for cookies. Justin knows May has put a bunch of cookies in the freezer in the basement because Ruby showed them to him. May says no, but Ruby insists Justin should be allowed a simple cookie. May and Ruby shout at one another for a moment, but Ruby still encourages Justin to get a bag of cookies.

Justin takes two bags of cookies and joins his father on the couch with them. May becomes angry and grabs Ruth's arm, tearing her dress, to drag her into the living room. Ruth becomes angry and claws out at both May and Ruby, demanding they stop fighting because it has been such a nice day and this was such a trivial thing. Ruth's reaction causes Ruby to snap. Ruby beats Ruth over the head and back with a poker from the fireplace. When May interferes, Ruby chases her first into the kitchen and then the basement. Ruth steps out the front door but realizes she must go back for Justin and May. Ruth finds Justin on the steps in the basement, watching as his father beats and stabs his grandmother.

Ruth pulls Ruby off May, but not until she has seen him strangle her to death. Ruby turns on Ruth again. Ruth manages to get outside where Ruby follows, beating her until her remembers the baby she still carries in her womb. Ruby stops and goes back into the house. Somehow Ruth makes it to a neighbor's house where they call the police. Ruby is arrested and Ruth is taken to the hospital where she will remain for nearly a month. Ruby moves into Aunt Sid's house when she is released from the hospital where she must remain lying on her left side for the remainder of her pregnancy in order to keep her blood pressure under control.

As Ruth recovers, she struggles to figure out what went wrong and why. Ruth speaks with counselors; she sits with her preacher, and she receives visits from family and friends. None of this helps her understand or move past the overwhelming anger. Ruth knows Ruby was sick and there must have been warning signs, but she could not see that. Now Ruth must get used to a life without May to tell her what to do and without the man she loves, a man she can no longer see even though he is still alive and still her husband.