It is still too dark for Quentin to depart on his mysterious errand, so he sits on the front porch imagining Miss Rosa sitting in the dark in her black bonnet and shawl. Mr. Compson comes out of the house with a letter—a letter from Charles Bon to Judith Sutpen that Judith entrusted to Quentin's grandmother many decades ago. Mr. Compson tells Quentin about the relationship between Charles Bon and Henry Sutpen, how they met at the university, where Charles was a debonair, ironic, and indolent man, looked up to by the local students, and how Henry fixated on him and imitated his appearance and behavior. When Charles went home for Christmas with Henry in 1859, speculation began—originating largely with Ellen—that Charles and Judith were to be engaged. Then Charles left for New Orleans, followed closely by Thomas Sutpen, and the next Christmas, Henry Sutpen was renouncing his birthright and fleeing Sutpen's Hundred with his friend.
Mr. Compson tries to imagine the confrontation between Henry and his father that led to the break, and describes a scene, behind closed doors, in the library at Sutpen's Hundred, during which Thomas announced to Henry that he refused to allow Charles to marry Judith, because he had discovered in 1859 that Bon was secretly keeping a octoroon (a woman with a "drop" of negro blood; technically, a woman who was one-eighth black) mistress in New Orleans, to whom he was probably already married. Henry refused to believe it, sided with his friend over his father, and abandoned Sutpen's Hundred. He went to New Orleans with Charles, who slowly indoctrinated him into the pleasures and corruptions of life in the sultry French-influenced city before revealing to him that he was, in fact, married to a French-negro courtesan, whom he also owned, and whom he had obtained in a strange underground circle of women raised specifically to be won by wealthy men. Bon discounted the marriage as a sham and reminded Henry that the woman, as a "nigger," was without rights—she did not "count" as his wife. But Henry was nevertheless shattered and enraged: he wanted to believe his friend, but felt pulled apart by inner conflict.
Then the war broke out. Henry and Charles Bon enlisted in a company, where Bon was quickly promoted to lieutenant. Henry remained a private, and refused to allow Bon to write to Judith while he tried to decide what to do. Mr. Compson hints to Quentin that Henry's fascination with Bon had sexual overtones, which may have spurred him to see Bon married to his sister; and also hints that Henry's deep connection with his sister had overtones of incestuous desire, which may have spurred him to see her married to his friend. In any event, after four years of fighting, life at Sutpen's Hundred, like life all over the South, was reduced to a scrabble for food and sustenance: Sutpen, a colonel, was off fighting; Judith kept a garden to feed herself and Clytie; Wash Jones squatted in the rotten fishing camp by the river and occasionally brought food to them.
After four years of fighting, Bon finally wrote Judith a letter—the enigmatic document that Quentin now holds. The letter, which Quentin reads, is a statement of Bon's intention to find Judith and marry her ("We have waited long enough," he wrote)—though he also wrote that he could not say when he would come, because he did not know himself. Mr. Compson describes how Judith and Clytie made a wedding gown out of scraps and rags after Judith received the letter; and Quentin imagines the scene before the gates at Sutpen's Hundred, Henry warning Bon not to come past the shadow of the post, Bon warning Henry that he was going to pass it. The next thing Mr. Compson describes is Wash Jones sitting on his mule outside Rosa Coldfield’s house, shouting to Miss Rosa that Henry Sutpen has killed Charles Bon.
This section is important because it clarifies and deepens our understanding of the relationship between Charles Bon and Henry Sutpen, and further clarifies our sense of Mr. Compson as a speculative, analytical thinker to whom everything is a sign of the predestined doom of men great and small. But this is also the most difficult section in the novel in some ways, because Mr. Compson's description of events is based on incomplete information, and is therefore misleading. As we will learn in subsequent chapters, Thomas Sutpen did not ride to New Orleans simply to investigate Bon, and did not merely discover that he was keeping an octoroon mistress or wife whom he also seemed to "own." Sutpen rode to New Orleans because he recognized Charles Bon as his own son, his child with the part-negro daughter of the Haitian plantation owner and Sutpen's first wife; if Bon married Judith, Sutpen's daughter would be marrying not only a man with negro blood, but her own half-brother.
Mr. Compson is also wrong when he imagines Henry's confrontation with his father to be centered on the problem of Bon's mistress; the break actually occurred, as Quentin and Shreve later realize, when Sutpen told Henry that Bon was his brother. During their subsequent trip to New Orleans, then, Bon was unlikely to have worried much about showing Henry his mistress/wife; Henry probably would have taken her as lightly as Bon did. But Mr. Compson does not know at this point that Bon was Sutpen's son, or that Bon's mother had negro blood, and his analysis is limited by his lack of knowledge. He tries to construct a whole picture but cannot.