As each character moves away from childhood innocence, the complexity of adult sexuality initiates unsettling insights into the reality of animal urges. The novel offers only one example of healthy sexual attraction—Kathleen’s ecstatic relationship with Rose. Otherwise, sexuality in the novel is defined more by lust than by the romantic ideals of respect, communication, trust, and support. Even relatively stabilizing relationships are either sustained by lies and secrets, or cool into indifference or oppression. Fittingly for the novel’s interest in Catholic dogma, sexual passion is a problem, typically leading to moral downfall and damnation. The novel links sexuality to the Catholic bugaboos of devils and damnation: Sex is a violation, a taboo, a dirty secret, or a sin; the children it creates suffer and die, while their parents face the shame of illegitimacy or the criminal trespass of having a relationship with someone of another race. One by one, the Pipers replay the fall of Adam and Eve into sin.

Given the powerful influence of Catholicism, the Piper clan never views sexual desire as healthy or miraculous. James is driven by pedophilia. His pursuit of the 12-year-old Materia is more predatory than romantic; once she matures into a teenager, his desire for her cools.