Thirteen-year-old Jessie Bollier, his widowed mother, and his sister live in a one-room home in a poor quarter of New Orleans in 1840. His mother makes a meager wage sewing dresses, and Jessie plays his fife to make a few pennies. He dreams of being rich someday, and although he is curious about the lives of slaves he sees, he is forbidden to visit the slave market and knows little about their daily existence. His mother tells him that despite his family's grinding poverty,
there were souls whose fates were so terrible in comparison to ours, that we should consider ourselves among the fortunate of the earth. I knew she was thinking of the slaves who were sold daily so close to where we lived.
When his mother has to make a dress in a hurry, she sends Jessie out to his aunt's house to get some candles so she can stay up late to sew, but on the way home from this errand, two sailors who have seen him playing his fife kidnap him.
Their ship is The Moonlight, a ship bound for Africa, under Captain Cawthorne, a man so brutal that when he meets Jessie, he bites Jessie's ear hard enough to draw blood. Captain Cawthorne tells Jessie that The Moonlight is a slave ship, involved in a "lucrative and God-granted trade," and that anyone who tries to interfere with it is a pirate. Jessie will play his fife to make the slaves "dance" once they are on board; this exercise will keep them strong and fit so that they will bring in more money when they are sold. In addition, he is expected to help around the ship.
Jessie meets Ned Spark, the ship's carpenter and occasional doctor, who professes to be a Christian but who will profit from the slave ship's voyage as much as the rest of the crew, including the ill-tempered cook; Nick Spark, the Mate, who is as cruel as the captain; and Ben Stout, who says he is sorry for Jessie's kidnapping, talks kindly to him, and gives him extra clothes and a piece of bread.
Once Jessie settles in, he notices that Purvis, who is a good sailor despite his rough manners and teasing sense of humor, is always busy, and he realizes that even though Purvis is one of the men who kidnapped him, he can trust him. Purvis tells Jessie that other ships will try and stop the slave ship from completing its journey. The British, who are against slavery, will board the ship and confiscate the slaves and the profits.
Until now, Jessie has been confused by the crew, who defend the trade, saying that so many ships are involved in it that the laws against it don't matter. Claudius Sharkey, a crewmember, tells Jessie that in addition to the British cruisers that make the trade dangerous, American ships also patrol against importers of slaves. However, the possible profit from these voyages outweighs the danger: "He spread his arms as wide as he could to show me the money the smugglers made after they'd taken the slaves inland and sold them."
Although Ben Stout has been kind to him, Jessie doesn't trust him. Instead, he likes Purvis: "Purvis, with his horrible coarse jokes, his bawling and cursing, Purvis, whom I trusted."
One morning, at dawn, he sees a sailor sneaking forward on the ship, and returning with an egg—part of the captain's private food supply. He is not sure who the sailor is, and soon Purvis is named as the culprit, tied up by Ben Stout and another sailor, and brutally flogged and then hung from the rigging. Later, he finds out that Stout stole the egg, and was happy when Purvis was blamed. When he asks Purvis why he didn't deny being the thief, Purvis says, "The officers of this ship would not care what the truth was."
The Bight of Benin
When the ship arrives off the coast of Africa, all the preparations for taking on slaves are completed. They go up and down the coast, and the captain goes out at night in a small boat and deals with the African chiefs who are selling the slaves.
Jessie is sick of being on the ship, sick of what he learns about the slave trade, and when Purvis asks him to help set up a tarp to provide shade for the slaves when they eat their meals, he refuses: "nearly senseless with rage ... I considered casting myself over the side and confounding them all!" But he gives in because he believes that no one on the ship would save him, and he would die. "I went slowly toward Purvis, feeling a shame I'd never felt before," he says.
Later, when he protests against the slave trade, Purvis becomes violently angry, and tells Jessie that his own Irish ancestors came to America in ships no better than the slave ships—"locked up in a hold for the whole voyage where they might have died of sickness and suffocation ... Do you know my father was haunted all his days by the memory of those who died before his eyes in that ship, and were flung into the sea? And you dare speak of my parents in the same breath with these [slaves]!"
Jessie wonders how Purvis can be so angry about the conditions his parents traveled under, and at the same time fail to see how it's wrong to treat the slaves like this. But...