East of Eden is the story of the Trask and Hamilton families, both of whom live primarily in the Salinas Valley region of California. The families are interwoven and experience intense dysfunction over a period ranging from the turn of the century to the end of the First World War. It deals with themes of family, forgiveness, peace, and redemption. It also spends a great deal of time considering the devastation caused by the War.
The story is primarily set in the Salinas Valley, California, between the beginning of the twentieth century and the end of World War I, though some chapters are set in Connecticut and Massachusetts, and the story goes as far back as the American Civil War.
In the beginning of East of Eden , before introducing his characters, Steinbeck carefully establishes the setting with a description of the Salinas Valley in Central California.
Then he outlines the story of the warmhearted inventor and farmer Samuel Hamilton and his wife Liza, immigrants from Ireland. He describes how they raise their nine children on a rough, infertile piece of land. As the Hamilton children begin to grow up and leave the nest, a wealthy stranger, Adam Trask, purchases the best ranch in the Valley.
Adam's life is seen in a long, intricate flashback. We see his tumultuous childhood on a farm in Connecticut and the brutal treatment he endured from his younger but stronger half-brother, Charles. Adam and Charles's father, Cyrus, was a Union Civil War veteran who was wounded in his very first battle and unable (or perhaps unwilling) to return to service; he nonetheless becomes an expert "armchair general" who uses his intellectual knowledge of military affairs and wounded-veteran status to become a military adviser in Washington, D.C. As a young man, Adam spent his time first in the military and then wandering the country. He was caught for vagrancy, escaped from a chain gang, and burgled a store for clothing to use as a disguise. Later he wires Charles for $100 to pay for the clothes he stole. After Adam finally makes his way home to their farm, Charles reveals that Cyrus had died and left them an inheritance of $50,000 each. Charles is torn with fear that Cyrus did not come by the money honestly.
A parallel story introduces a girl named Cathy Ames, who grows up in a town not far from the brothers' family farm. Cathy is described as having a "malformed soul"; she is an evil woman who delights in using and destroying people. She leaves home one evening after setting fire to her family's home, killing both of her parents. She becomes a whoremaster's mistress, but he beats her viciously upon realizing that she is using him, and leaves her to die on Adam and Charles's doorstep. Although Charles is repulsed by her, Adam, unaware of her past, falls in love with and marries her. However, unbeknownst to Adam, Cathy seduces Charles at the time of her marriage and the beginning of Cathy's pregnancy with twins, leaving open the question of whether Adam or Charles is the twins' father.
Adam– newly wed and newly rich – now arrives in California and settles with the pregnant Cathy in the Salinas Valley, near the Hamilton family ranch. Cathy does not want to be a mother or to stay in California, but Adam is so happy with his new life that he does not realize there is any problem. Shortly after Cathy gives birth to twin boys, she shoots Adam in the shoulder and flees. Adam recovers, but falls into a deep depression. He is roused out of it enough to name and raise his sons with the help of his Cantonese cook, Lee, and Samuel.
Lee becomes a good friend and adopted family member. Lee, Adam, and Samuel have long philosophical talks, particularly about the story of Cain and Abel, which Lee maintains has been incorrectly translated in English-language Bibles. Lee tells about how his relatives in San Francisco, a group of Chinese scholars, spent two years studying Hebrew so they might discover what the moral of the Cain and Abel story actually was. Their discovery that the Hebrew word "Timshel" means "thou mayest" becomes an important symbol in the novel, meaning that mankind is neither compelled to pursue sainthood nor doomed to sin, but rather has the power to choose.
Meanwhile, Cathy has become a prostitute at the most respectable brothel in the city of Salinas. She renames herself "Kate Albey" and embarks on a devious– and successful – plan to ingratiate herself with the madam, murder her, and inherit the business. She makes her new brothel infamous as a den of sexual sadism. After Charles dies of natural causes, Adam goes to see her to give her money Charles left her. Kate renounces him and the entire humanrace, and shows him pictures of the brothel's customers, all pillars of the community. Adam finally sees her for what she is, and pities her.
Adam's sons, Caleb "Cal" and Aron– echoing Cain and Abel – grow up oblivious of their mother's situation. They are opposites: Aron is virtuous and dutiful, Cal wild and rebellious. At a very early age, Aron meets a girl, Abra Bacon, who is from a well-to-do family, and the two fall in love. Although there are rumors around townthat Cal and Aron's mother is not dead but is actually still in Salinas, the boys do not yet know that she is Kate.
Samuel finally dies of old age and is mourned by the entire town. Inspired by Samuel's inventiveness, Adam starts an ill-fated business venture and loses almost all of the family fortune. The boys, particularly Aron, are horrified that their father is now the town laughingstock.
As the boys reach the end of their school days, Cal decides to pursue a career in farming and Aron goes to college to become an Episcopal priest. Cal, restless and tortured by guilt about his very human failings, shuns everyone around him and takes to wandering around town late at night. During one of these ramblings, he discovers that his mother is alive and the madam of a brothel. He goes to see her, and she spitefully tells him that they are just alike. Cal replies that she is simply afraid, and leaves.
Cal decides to "buy his father's love" by going into business with Samuel's son Will, who is now a successful automobile dealer. Cal's plan is to make his father's money back, capitalizing on World War I by selling beans grown in the Salinas Valley to nations in Europe for a considerable premium. He succeeds beyond his wildest expectations and wraps up a gift of $15,000 in cash which he plans to give to Adam at Thanksgiving.
Aron returns from Stanford for the holiday. There is tension in the air, because Aron has not yet told their father that he intends to drop out of college. Rather than let Aron steal the moment, Cal gives Adam the money at dinner, expecting his father to be proud of him. Adam refuses to accept it, however, and tells Cal to give it back to the poor farmers he exploited. Adam explains by saying,
I would have been so happy if you could have given me– well, what your brother has – pride in the thing he's doing, gladness in his progress. Money, even clean money, doesn't stack up with that.
In a fit of jealousy, Cal takes Aron to see their mother, knowing it will be a shock to him. Sure enough, Aron immediately sees Kate for who she is, and recoils from her in disgust. Racked with self-hatred, Kate signs her estate over to Aron and commits suicide. Aron, his idealistic worldview shattered, enlists in the Army to fight in World War I. He is killed in battle in the last year of the war, and Adam suffers a stroke upon hearing the news from Lee. Cal, who began a relationship with Abra after Aron went to war, tries to convince her to run away with him. She instead persuades him to return home.
The novel ends with Lee pleading with a bedridden and dying Adam to forgive his only remaining son. Adam responds by giving Cal his blessing in the form of the word Timshel .