Hiding below deck on the riverboat, James and Norman are discovered in the engine room by Brock, a black worker tending the furnace. Because James does not know whether Brock can be trusted, James immediately speaks in slave dialect and signals Norman to pose as James's white master. Norman, though disgusted by the role, uses white authority to silence Brock and keep him from reporting them.

To improve Norman's chances of moving through the boat unnoticed, James sends Norman to the forward hold to search steamer trunks for better clothes. Norman finds a mismatched outfit stolen from a passenger, and James notes that even filthy, bedraggled whiteness still gives Norman power over Brock. After Norman goes upstairs to look for food and information, Brock makes James shovel coal, claiming that anyone in the room must work or be reported to "Massa Corey," the overseer Brock fears.

As James labors in the extreme heat, Brock reveals how thoroughly he identifies with the engine and with serving his master. Brock says the engine room is his entire world, that he rarely leaves it, and that food is simply left for him outside the door. James grows increasingly disturbed by Brock's obedience and by the condition of the boiler, which Brock admits has begun making new banging noises and shaking.

Time passes while Brock sings and works, and James, hungry and exhausted, listens to Brock's devotion to both the boat and Corey. When Norman finally returns, James accidentally drops the slave speech in front of Brock, confirming Brock's suspicions that something is wrong. Away from Brock, Norman reports that Daniel Decatur Emmett is aboard the packed boat and that passengers are hurrying north because war appears to be beginning as slave states try to leave the Union.

James shares his belief that Brock may be serving an absent or even nonexistent "Massa Corey," suggesting that Brock has been left alone to keep the boat running. As James and Norman look back, Brock is shoveling frantically, the boiler screams at a higher pitch, and the engine's rhythm falters. The chapter ends with James and Norman realizing the boat itself may be in immediate danger.