The irony of Hiram's grandfather
Hiram doesn't understand racism. He hates to think that people might not like each other for something as inconsequential as race, but when he learns that his own father is a racist and a violent man who helped to kill Hiram's friend Emmett Till, then Hiram is stunned. He sees through that irony that his family is not immune to hateful ideas.
Emmett's drowning scare
Ironically, Emmett's real death is proceeded by a drowning scare, but Hiram saves him. The irony is that only Hiram would have saved him, it seems, because the town seems to hate Emmett from the start, perhaps because he is a brilliant person and he defies their racist stereotypes. Anyway, Hiram gets a chance to save him, before ironically, his work is undone by his own community, who turns around and kills him.
The irony of distance
When he is in Arizona, that is the first time he has distance from Mississippi, and he has the chance to re-examine the community. When he revisits the town, he realizes even more, because the distance between Arizona and Mississippi helped him to cleanse his pallet. Now, he isn't as close to his family and friends, because of the time and space they were apart, and this makes him more objective. Having the distance, he realizes that Mississippi is deeply troubled and broken because of racism. He had to leave before he could see it clearly.
The chain of abuse
Hiram learns about a tragic irony through the novel. The issue of abuse is touched on in the denouement, with the assumption that the grandfather's hatred was also used against Hiram's own father, because Hiram's father is not racist, so obviously there has been conflict on the point. The chain of abuse made it hard for Hiram to understand why his father was so extreme and impersonal, but it is because he was damaged by the hatred of a murderous man.
The irony of identity
Who is Hiram if not a part of his community? He disagrees with the racism and hatred that defines his community, but when he was a kid, he didn't even think about that or notice it really. He was ironically identified with a town that he ultimately resents for its bitter racism and violence against the Black community. He is forced to admit that his worldview was shaped by his community, and he must choose to become a person all his own if he hopes to extricate himself of their damage. He is certainly damaged by his community murdering his friend, Emmett.
