The irony of wealth and power
There is a dilemma between wealth and power in this novel. Although the wealthy and powerful are clearly the lawyers, the homeless man shows a type of power that none of the others have shown. He shows them the unmistakeable fear of human death, by pointing a gun at them. This heinous action signifies an irony about their lives—that they do not fear judgment.
The irony of violence
Violence was never necessary. It would have costed nearly nothing to help the homeless man instead of hurting him, but instead, they do violence. Then, when someone is waving a gun at people, he ends up being shot by a SWAT sniper, so violence is an easily excitable thing that spreads like wildfire. It doesn't work for anyone, and it leaves one person dead.
The irony of mistreatment
The homeless man is correct about his gripe, but not the severity of his situation. Because he hyperbolized his frustrations, he becomes like an archetypal icon of mistreatment. He is the one who wants justice. As a symbol for justice, he is a poor one and Brock is a good one, because Brock gets a confession out of the firm, whereas the victim himself only got himself killed.
The ironic confession
In a move that surely shocked every reader, the company simply admits they were wrong. Since the homeless man decided to threaten all of their lives with a gun, he is already dead because of his own actions, but yes, they were wrong to evict him illegally, and it is something they probably do to many, many poor people. The reader sees that in a way, the man was a martyr.
The irony of law
In the end, Brock finds peace by working for the homeless. He finds that law isn't really what most people think it is. It is a field of combat, and lawyers and wealthy men have more access to arms than most, so they win, and the powerful set the tone for what "justice" means anyway, so it always leans toward the wealthy and powerful. Brock says enough, and just quits.