Cora is a slave on a cotton plantation in Georgia. Life is nightmarish for all the slaves, but especially for Cora, as she is marginalized by the other Africans. Even greater pain awaits her as she grows up and becomes a woman. When Caesar arrives from Virginia and tells her about the Underground Railroad, the two decide to defy the enormous danger and escape. Things do not go as planned, and although they manage to find a station and head north, they are pursued.

In Whitehead's ingenious conception, the "Underground Railroad" is not just a metaphor - engineers and conductors have set up a secret network of tracks and tunnels underground. Cora and Caesar's first stop is South Carolina, in a town that initially seems like paradise but hides something sinister for its black residents. The worst part is that Ridgeway, the relentless slave catcher, is on their trail. Forced to flee again, Cora embarks on an incredible journey, seeking true freedom.