The title irony
The title refers to dramatic irony, because the metaphor of standing on the edge of water is a symbol for learning something. The waters are Dark, which is to say they are obscuring. In other words, the novel is about the encounter that Sue has with whatever will rise from the depths of the unknown. What has been concealed in dramatic irony of innocence will become known, and the experience will transform her. From chaos to order, from unknown to known, something emerges. What is it? It is human death.
The father's reaction
Sue Ellen is completely undone by the death of her friend. To her, it is an unfathomable reality. She is in religious epiphany when her father suggests that they toss her back in. That is the most ironic response possible from the person Sue is closest to in the world. What the irony shows is that not only are adults familiar with death, they are so constantly threatened and exposed by death that some people get used to it. This is the surprising attitude that says, "Well, what were you expecting? People die, honey! Get used to it." To Sue Ellen, this is a flagrant blasphemy. She becomes like Antigone.
The meaningless quest
Just as Antigone gives her life to bury the dead, so also Sue Ellen ventures into the wilderness (which she just learned from experience can be violent and deadly). Why? For the same reason—to give a loved one a proper burial. In this case, that means laying May Lynn's ashes to rest in California, in Hollywood where she wanted to live. The irony of the quest is that May Lynn is already dead, so in some senses, the quest is meaningless. Then again, there is an ironic way in which the quest is meaningful, especially when they discover how she died.
The surprise of community
Sue goes on this quest with Terry and Jinx. The crew is unlikely. Sue Ellen is a outdoorsy, nature-loving girl with a big heart and a passionate spirit. Terry is a gay boy whose family ostracizes him after his mother marries a homophobic man with homophobic sons of his own. Jinx is a young black girl who longs to feel powerful, but struggles with self-esteem. Together, they seem perfectly random, but actually, their journey teaches them each lessons from the others. In the end, Terry realizes he isn't alone after all, and that people will accept him for who he is. For Jinx, she realizes that she is worthy of praise and attention, and for Sue, she finds meaning in life despite life's cruelties.
Redemption as a boon
Ironically, Sue's "boon," the reward for her adventure, is not really for her. Granted, she does get clarity and peace, but her boon is knowledge gained about May's life. In other words, the reward for Sue's traveling is that she can restore May Lynn's reputation. Some people believe she drowned herself because she felt she wouldn't make it in Hollywood. Sue realizes that actually, May's death was a straight-up homicide. Learning that some people murder other people sometimes is also a boon, and again, it is ironic.
