Caste: The Origins of Our Discontents by Isabel Wilkerson opens with a passage in italicized type analyzing an old photograph that depicts hundreds of German workers joyfully saluting their leader, Adolf Hitler. In one corner of the frame is a lone figure who stands out because he is not saluting, having come to despise the Nazis for the way their anti-Semitic policies have affected his fiancée.

Wilkerson then begins part 1 by describing two major events that took place in 2016. One was an unlikely anthrax outbreak in Siberia caused by the effects of global warming, and the other was the election of Donald Trump as United States president after a campaign based on a message of hate and division that unleashed long-simmering toxic forces from below the surface of American society. The rest of part 1 introduces four important metaphors that Wilkerson uses to establish the problem of America’s race-based caste system. She first describes the country as a sick patient visiting a doctor, who must take an honest and detailed history in order to diagnose the ailment and prescribe a remedy. Next, Wilkerson describes America as an old house, badly in need of expensive repairs that the owners have been avoiding due to the cost and inconvenience. In this model, caste is the invisible framework beneath the rotting surfaces that must be examined and repaired before the structure can be declared sound. Wilkerson then tells the story of Martin Luther King Jr.’s 1959 visit to India as a guest of President Nehru and King’s learning of his heroic standing among India’s Dalits, or “untouchables,” whose servile, subordinated lives reminded him that African Americans were the United States’s own “untouchable” servant class. Finally, in order to illustrate both caste’s deep coding in the human mind and how resistant people are to confronting and breaking free of its illusions, Wilkerson compares caste’s predominance to the movie The Matrix and its bleak portrayal of existence as a computer simulation.

In part 2, "The Arbitrary Construction of Human Division,” Wilkerson gives historical context to the US’s race-based social hierarchy, which she traces back to 1619 and the establishment of an unprecedented form of generational, inescapable human enslavement based on skin color. This created the formerly nonexistent categories of “white” and “Black” that have been the definitive social determinant in the US since then. The American fixation on race limits people’s ability to see beyond their biases and coding, leading them to instead merely see what Wilkerson calls the “container” and resulting in misperceptions she has personally experienced. Taking genetic research as a basis, Wilkerson goes on to refute the value of race as a category. She then examines India’s ancient caste system, comparing and contrasting it with America’s and highlighting some key distinctions. Wilkerson’s other main example of a race-based caste system is Nazi Germany, where race laws were based on the American example the Nazi party so admired and at whose extremity they marveled.

In part 3, “The Eight Pillars of Caste,” Wilkerson outlines what she determines to be the essential, universal elements of caste systems regardless of their formal or operational differences, with particular attention to the United States, India, and Nazi Germany. In keeping with her architectural metaphor, she describes these structural elements as “pillars” and identifies eight:

1. The belief that caste is ordained by divine will
2. The heritability of caste
3. The dominant caste’s control of subordinate bloodlines
4. Obsession with purity versus pollution
5. Occupational restrictions on subordinates
6. Dehumanization of subordinates
7. Terror as a means of caste enforcement 
8. The belief in inherent superiority versus inferiority

Part 4, “The Tentacles of Caste,” explores the reach and crushing grip of false social divisions. While researching this book, Wilkerson became newly aware of the patterns of ingrained caste-based behavior among her Indian peers and met an upper-class Indian man from whose experiences and insights Wilkerson learned much about the practical implications of caste, despite the system having been officially prohibited. She then highlights the phenomenon that drove the outcome of the 2016 election: the perceived threat to the status of lower-class white Americans by people of color and immigrants. Not only is this the source of the vicious race-baiting of the last few years, but the physical stress related to this mental state has also been causing increased risk of chronic illness and decreased life expectancy for working-class white people, in a trend going against general health outcomes for other groups. She also identifies the African American subordinate caste as functioning as permanent scapegoats to receive blame for society’s problems, allowing white people to feel morally superior and further justifying the oppression and marginalization of those unlike them. Finally, she illustrates with multiple examples how the patriarchal privilege of the dominant caste continues to extend into Black private lives and family business, often involving the police, and explores the self-perpetuating nature of intra-caste conflict that maintains downward exclusion at all levels.

Similar to the book's opening passage, part 5, “The Consequences of Hate,” begins with a description of a film clip showing Hitler’s triumphant return to Berlin, the streets crowded with jubilant citizens. Wilkerson reminds the reader that these people were ordinary human beings who loved their country and were susceptible to manipulation of truth. Germany is also an example of the blinding narcissism, or self-interest, of caste that allows for the majority’s tolerance of extreme political movements. These consequences are felt every day by Wilkerson and other upper-class subordinates through vexing indignities that sometimes prove tragic and deadly for others without their status. Wilkerson then discusses the status-related health issues of African Americans, providing a salient contrast to her earlier discussion of declining health among the dominant caste. The educated, professional, or otherwise accomplished class of subordinate-caste people, she writes, must work twice as hard to be taken half as seriously—which, coupled with the daily stress of being on the “front lines” of the social clash, has led to an increase in the same chronic lifestyle-related illnesses that afflict lower-class whites.

Part six, “Backlash,” describes the racially charged social and political reaction to Barack Obama’s election in 2008, which many took as a signal for the end of racial discrimination in the United States. Instead, race-based fears and anxieties that had been shadowy currents in American society since the end of the Civil War gained momentum and broke through the surface, which Wilkerson gives as context for the series of well-publicized killings of young Black men and boys beginning in 2012. One of the main causes of the majority caste’s resentment, she reveals, is their dread of 2042, when, for the first time, the majority of US citizens will be people of color. This fact endangers the primacy of the traditional dominant caste and fuels the recent mainstream resurgence of white supremacist groups. The violent resistance to recent efforts to remove public symbols of the Confederacy has been cloaked in benign, sentimental language but actually represents the unwillingness of the dominant caste to relinquish their cherished status quo.

In the final chapters and epilogue, Wilkerson imagines a world without caste in which all people would be free to fulfill their individual potential regardless of superficial physical characteristics based on the accident of birth. Wilkerson uses Albert Einstein as an example of someone whose conscience would not allow him to be complacent in his privilege as long as others were persecuted, a conviction that led him to vocal criticism of American society and devotion to social justice activism. Einstein exhibits the kind of “radical empathy” that Wilkerson calls for as a solution to American social divisions, and the author describes her own and others’ personal experiences with its transformative potential.