The bad good thing
When Selina's family discovers a small windfall in the form of an inheritance of property in Barbados, it is a good thing that effects the family in an adverse way. The irony of a bad good thing is that in the wrong situation, a windfall can amplify disagreements in the house. Money is one of the most tense subjects in any marriage, but way more so when money is tight or when a family is living check-to-check. The indulgent father is ill-suited to use the money responsibly, and he wants a lavish mansion that is not feasible. The mother wants a reasonable step forward in the financial well-being of the family.
Parental loyalty and dysfunction
The daughters get caught in the complicated network of loyalty and dysfunction. Dysfunction has made the parents act like free agents instead of agreeing about their plans in their marriage. In this fractured dynamic, the parents are like antithetical poles that drag the sisters in opposite directions. Each girl sides with one parent more than the other, and they embody the dysfunction which is actually their own inheritance. The parents are ironic because their selfishness makes their children unhealthy.
The ironic downfall
When the reader sees the volatility of the father, a standard downfall is sort of expected. For instance, perhaps the father will have an episode of aggression and anger that leads to violence and his incarceration. That is an example of a typical plot line. Instead, the reader finds out that he is ostracized by his community, that he loses an arm in an accident, joins a cult, gets raided by the government, and drown in the ocean. The irony of his colorful fate is also part of the children's inheritance. They too can expect wild and atypical journeys as they move through life.
Maturity and drama
Selina is well-aware of her own burgeoning maturity. More and more, she finds herself able to draw judgments about her parents' behavior (the ironic opposite of her sister's point of view, as if nature had programmed them to go in opposite directions). Selina experiences her fear of the unknown in the dramatic irony of her menstrual cycle. She suspects it will happen, and then it does happen, and in both situations, the drama is clear; she is unable to determine what it means that she should have to endure that aspect of nature.
The missing conviction
She grows up to feel a general anhedonia. She enjoys relationships for a while, but she does not find herself attracted to marriage or commitment. She is burned out on family by a difficult childhood. Inherently, this makes her prone to repeat dysfunctional problems, and so she just disengages suddenly. The finale of the book is the ironic discovery that Selina does not feel desire to accomplish any particular goal. She finds life is meaningless, and quits her endeavors, considering a return to Barbados where she might rediscover her joie de vive by a heroic venture to the land of her ancestors (an archetypal literary motif).
