Ten years have now passed since Adam, Samuel, and Lee named the Trask children. In the interim, Samuel's favorite child and "greatest joy", Una, has married a photographer named Anderson and moved with him to Oregon. Her husband keeps Una in abject poverty, and she eventually dies (perhaps having committed suicide) after living for years in conditions of hard physical labor and near starvation. Una's death casts Samuel into a depression from which even he cannot emerge. He wrongfully blames himself for having neglected his beloved daughter. This is the beginning of his decline: "his young skin turned old, his clear eyes dulled." Samuel's other eight children (including Steinbeck's mother, Olive) meet to discuss what should be done about their aging parents, and decide to have them visit in turns under the guise of wishing to spend more time with them. Tom Hamilton, upset about the idea of his parents leaving the family farm, sees this strategy as insulting to his father, but Samuel assures him that he knows quite well what is going on, and that he has neither the energy nor the inclination to fight it: "I know why I'm going - and, Tom, I know where I'm going, and I am content." The "why" and the "where" here indicate that Samuel knows full well that he will die shortly. He visits his old neighbors, who are strewn about the Salinas Valley, and saves the Trask ranch for last. On what will be his final visit, he finds that the twins he once delivered are now eleven years old. Once again, the story of Cain and Abel comes up over drinks. Lee explains that in the ten year hiatus, he has studied the Cain and Abel story in Genesis 4: 1-16 with four Chinese sages and a rabbi in San Francisco. In one biblical translation, Lee explains, God promises Cain that in time he will overcome sin, but in another translation, God orders Cain to overcome sin. After ten years of intellectual sparring, the scholars conclude that both translations are in error and that, indeed, the Hebrew word timshel, the verb in question, actually means "thou mayest" - in other words, thou mayest rule over sin. As Samuel declares, it is "the choice of winning." Samuel immediately grasps the meaning of the term, to Lee's great delight: God simply gave human beings the ability to choose good over evil. By choosing good, they can rule over evil. At this point, Samuel makes a decision about a secret that has been plaguing him for years. Now able to look death directly in the face, Samuel decides to save Adam from his ongoing apathy and dejection by informing him that his wife still resides in Salinas, where she runs a notorious whorehouse. Adam, unable to accept what Samuel tells him, runs away into the night, screaming in horror.
Adam attends Samuel's funeral, which is held soon after his death on March 15th, the infamous ides of March. Afterwards, he drinks at the Abbot House bar before going to Kate's brothel to finally confront his wife. For the first time, he sees Cathy/Kate not as a beautiful young woman, but as a vile monster. At last, he feels free, and his dark, depressive mood lifts. Although Kate tempts him sexually, she holds no more power over him. To demonstrate her power over others, she shows him photographs of some of the most important men in town in compromising sexual situations. She plans on blackmailing these men in an effort to raise cash so she can move to New York City. All men, Cathy cries out to Adam, are nasty, selfish brutes. She expects Adam to be impressed with her cleverness, but he is absolutely horrified. He tells her, "you hate something in them you can't understand. You don't hate their evil. You hate the good in them you can't get at." At this point, she screams at him like an animal, declaring that he will one day plead with her to take him back. He tries to leave, and she becomes even more hysterical, screaming at him that she slept with his brother, Charles, and that Adam may not even be the children's father. In response, Adam says that the boys' true parentage simply doesn't matter to him. Before returning home, he decides to buy a car from Samuel's son, Will Hamilton, who is quickly becoming the most important businessman in town. When Adam returns home, he informs Lee about Kate's state of mind: "In some strange way my eyes of cleared." Lee, who sees with great relief that Adam has finally thrown off his cloud of depression, informs Adam that the time has come for him to fulfill his dream of opening a bookstore in San Francisco. Adam agrees, but asks him to remain until he can get his affairs in order. Lee feels confident now that he can begin accomplishing his own dreams instead of spending all his time caring for the Trask twins.
The dark-haired child, Caleb Trask ("Cal"), always wants to fight, while his blonde-haired brother, Aron, only fights when provoked. One day while out hunting rabbits with bows and arrows, they twins argue over who should take credit for having shot a rabbit. Aron is childlike, light-hearted, and naive, while Cal is dark, clever, and manipulative. Cal confides in Aron a secret he overheard from some men in King City: their mother isn't dead after all, but is in fact living in Salinas. Aron, who believes that his mother is in heaven, becomes extremely upset, and vehemently denies his brother's allegation. Cal joyfully realizes that he has found the sharpest weapon of all for controlling his brother: Aron's love for their missing mother. The boys return home to find unexpected company: the Bacons and their beautiful eleven year-old daughter, Abra, have asked for shelter from a sudden rain storm. As the children play outside, Mr. and Mrs. Bacon suggest that Adam move the family to Salinas so the boys can attend school. The boys are completely tongue-tied by the beautiful Abra. Adam goes to his room to get the dead rabbit they killed, placing it tenderly in a box to give to the girl as a gift. He includes a note asking Abra to marry him. Meanwhile, the manipulative Cal scares Abra into thinking there is a snake in the box: she tosses it away, and unknowingly breaks young Aron's heart.
Adam, whose depression has finally lifted, surprises the boys during dinner that night by talking to them. Cal takes this opportunity to inquire about his mother, saying that Abra wants to know where her grave is so that they can take her some flowers. Once again, Adam lies to the boys. Lee, who believes in honesty at all costs, strongly suggests that Adam tell the boys about their mother before they find out about her from strangers and come to hate their father for having kept the truth from them. Lee then shares his personal history: to repay a family debt, Lee's father was forced to leave China and move to America to become an indentured worker building railroads. Unbeknownst to her husband, Lee's mother disguised herself as a man so that she could accompany him to the United States. When they learned that she was pregnant, they planned on going into the mountains, but Lee's father broke his leg, and Lee's mother went into early labor. When the mob of workers found out that there was a woman amongst them, "they all went mad." The men gang-raped and killed Lee's mother shortly after she gave birth to Lee. With great humility, Lee goes on to say that Adam should not judge the men: "No child ever had such care as I." After Lee's story, Adam becomes melancholy and writes to Charles, inviting him to come to California for a visit. He tells him that he and Cathy have separated, that she lives in town, and that he sees her on occasion. A week following the arrival of his new car, Adam drives to the post office, where he finds a letter announcing the death of his brother. Just like their father Cyrus, Charles has left an inheritance of $100,000 to be divided between Adam and Cathy. Later that evening, Cal eavesdrops on a conversation between Adam and Lee, and learns that his mother is not only alive, but that she lives in Salinas and works in a whorehouse. Cal, horrified, drops to his knees and begs God for forgiveness and to make him a better person.
Steinbeck, who positions the biblical story of Cain and Abel at the center of East of Eden, explores the concept of timshel - the key to true redemption for the characters in the novel. After a ten-year hiatus, Samuel, Adam, and Lee return to the philosophical conversation they previously debated at length. Lee tells the other two gentlemen that for the last ten years he has been studying the Cain and Abel story in Genesis 4: 1-16 with a group of scholars in San Francisco. In one biblical translation, Lee points out, Cain is promised by God that he will in time overcome sin. This interpretation casts Cain into a passive light: he is wholly without free will. A different translation states that God orders Cain to overcome sin, implying a similar lack of individual agency. These two translations both preclude the possibility of redemption. Lee goes on to explain that both translations are in error, and that the Hebrew verb timshel ("thou mayest") suggests a different interpretation of the events. God, Lee believes, told Cain that he could make the choice to overcome sin. Mankind has free will, and is not predestined to repeat the sins of the fathers. Samuel is quick to appreciate this concept, and utilizes it as a means to save his friend, Adam Trask. Adam, he feels, must know the truth if he is to be free to choose a different sort of life.
Adam is given the choice to live his life clearly, or to remain bogged down in apathy, depression, and longing for Cathy. Thanks to Lee and Samuel, Adam gains agency through his realization of the novel's central concept, timshel, and by learning that his wife is still living in Salinas. Finally, he can choose to live differently, and to see Kate as the monster she is and not as his pretty, young, vulnerable wife. He finds within himself the power to resist her feminine wiles. Indeed, when they at last meet face-to-face he finds that he has all the power, and that for once she is powerless. At this point, Adam finally becomes a real father, a father in the vein of Samuel Hamilton. Now that he has become a good father, it doesn't even matter to Adam that the twins might not be his. His decision to purchase a car and learn to drive it signifies his willingness to move ahead: it is the beginning of a new era for the Trasks. Lee also realizes that he is finally free to move. The deep freeze imparted by the evil ice witch Kate has melted at last.
In addition to the concept of timshel, the novel's central thematic concern - the battle between goodness and evil - rages on in the new generation, and the issue of tainted money once more comes to light. Aron is innocent and good-hearted, and turns away from anything even suggestive of evil. When faced with the truth about his mother, he rejects it entirely, and doesn't even want to discuss the possibility that his mother might still be alive. To consider this possibility would mean that his father might have lied, and this is something he cannot fathom. He is also tenderhearted: he instantly falls in love with Abra, immediately idealizing her and pursuing her hand in marriage. Simply put, Aron is pure at heart. Cal, on the other hand, is darker not just in physiognomy, but also in temperament. He is manipulative, disobedient, seeks out trouble, and has an insatiable curiosity. While Aron accepts what is told to him about his mother at face value, Cal questions everything, and seeks to discover the truth for himself. The reader is left wondering whether the Cain and Abel paradigm will repeat itself. Lee's family saga is a testament to familial love and sacrifice, an illustration of how family members can and should treat one another. Will Cal attempt to kill Aron, as Charles once attempted to kill Adam? Cal's childish jealousy of Aron stems from the fact that Abra favors Aron over him, but hope is found in the fact that Cal is horrified by his actions, and prays for the strength to change.
Money continually interferes with Cal's ability to choose goodness over evil. From early on in life, Cal is attracted to money. Indeed, the first thing that springs to mind when he hears of his uncle's death is money, while Aron thinks about putting flowers on the grave. The ill-gained inheritance Cyrus left to Adam and Charles comes into play once again in this section: their grandfather's "original sin" is revisited upon Cyrus's descendants. Charles leaves Adam and Cathy $100,000, having doubled his inheritance through miserly means. It is worth noting that despite the fact that both inheritances have been earned through corrupt means, neither Adam nor Charles even momentarily considers returning the money. The issue of tainted money circulates throughout the entire novel.