Cora is a slave on a cotton plantation in Georgia. All the slaves lead a hellish existence, but Cora has it worse than most; she is an outcast even among her fellow Africans and she is approaching womanhood, where it is clear even greater pain awaits. When Caesar, a slave recently arrived from Virginia, tells her about the Underground Railroad, they take the perilous decision to escape to the North.

In Whitehead's razor-sharp imagining of the antebellum South, the Underground Railroad has assumed a physical form: a dilapidated box car pulled along subterranean tracks by a steam locomotive, picking up fugitives wherever it can. Cora and Caesar's first stop is South Carolina, in a city that initially seems like a haven. But its placid surface masks an infernal scheme designed for its unknowing black inhabitants. And even worse: Ridgeway, the relentless slave catcher sent to find Cora, is close on their heels. Forced to flee again, Cora embarks on a harrowing flight, state by state, seeking true freedom.