The Irony of Mathu's Innocence
Although all of the plantation hands and Candy defend Mathu by accepting blame themselves, they all truly believe he is guilty for Beau's murder. The irony is that Mathu didn't murder him. Charlie did. Even Mathu's own friends preemptively presumed his guilt, despite their continued loyalty.
The Irony of Candy's Defense
Candy tells Miss Merle that she murdered Beau. Merle doesn't believe her, but she is persuaded by Candy's vehemence in the defense. As partial (now full) overseer, Candy is responsible for maintaining the welfare of the plantation. Although it would appear that finding the rightful murderer is her top priority, for the good of the plantation she actually takes on the responsibility for the murder herself. In this way she preserves morale and continues to fulfill her role as emissary between the owner and the employees, honoring the trust she has between both parties.
The Irony of Gil's Friendship with Cal
Gil has cultivated a partnership with Cal in school, despite his own family's historically racial mindset. When he learns of his brother's death, however, he turns on Cal and treats him badly. Somehow the knowledge of his brother's death is enough to bring back Gil's former racist ideas in full effect.
The Irony of the Shootout
When Gil says he does not support an attack on the plantation, he convinces Fix not to go as well. This is noble effort, but the violence will still take place. Luke hears that Fix has backed out and decides to take the issue of avenging Beau's death upon himself. But mostly he just wants to participate in an act of violence.
The Irony of Charlie's Confession
Charlie returns from the woods just in time to prevent the sheriff from taking Mathu away. Ironically, he gains nothing from this noble sacrifice because Luke and his crew have already arrive, and they will not leave without violence. Luke, personally, ends up killing Charlie (and also being killed by Charlie). While he had hoped to serve out his trial honorably, he loses his life over the affair.
