The irony of accidental murder
Although Cal Barker didn't mean to murder an innocent girl, he did so anyway by allowing his violent temper to get what it wanted from him. He ends up setting off a chain of consequences that leads to Andrea's horrifying experience of being burned alive, and the burns she sustains end up claiming her life. The irony is that his intent had almost nothing to do with the consequences of his actions.
The irony of violence circles
Barker is angry about injustice when he does violence, causing more injustice. That is ironic, because it means that as evil goes, it gets more pernicious, because violence escalates. No one who wants vengeance is going to be satisfied letting the past stay in the past. But, for that means that more and more tragedy happens, for no reason.
The irony of Barker's daughter
Ironically, Cal Barker's own daughter comes to his victim's family in a time of need. They choose to forgive her, but that is somewhat ironic, given that other characters who have been harmed by others have chosen to view those who harmed them as enemies. Obviously, they don't consider the Barkers' to be enemies, because they feel comforted by Cal's daughter.
The irony of time
Although the clock goes in a circle, it doesn't go in a circle forever. Eventually, each one of these characters will meet their death, so when someone receives the gift of their grandfather's Timepiece, a literal grandfather clock, that is an ironic depiction of time, because "time" was a gift given by someone who could not prolong their own time to begin with.
The irony of tragedy
Although tragedy is something that no one in this book is immune to, there is some tragedy that has human origin, and some that does not. The irony of the depiction of tragedy in this book is that Andrea died, not by her fault but by other's, and that tragedy actually starts early, as early as her random ailments in childhood. Tragedy does not effect everyone equally all the time, but ultimately, no one is immune, it seems.
