Incest plays a large role in Tender is the Night. Fitzgerald is conscious of its function as showing a violation of norms. Its function is to reveal a world where what should be pure is corrupted. This is the case with Nicole. After her mother died, Nicole's world was already jarred out from its emotional frame of reference. When Devereux Warren sexually abuses his daughter, it causes immeasurable damage. The function of incest is to show the extent of scarring on an individual. Nicole is unable to fully recover from what her father does to her. Incest becomes the mark by which human beings who profess to love another commit some of the worst and most painful of crimes. It is a transgression in the private realm, reflecting how private cruelty can constitute some of the most brutal of actions. The father that violates the daughter scars her for life.
The looming aspect of incest is another way that it functions in the novel. Nicole is never really able to fully escape the grasp of her father's incestuous relationship with her. It undermined her psychologically, causing her to land in the Zurich clinic in the first place. It is here where she meets Dick. Their entire relationship is predicated off of an improper frame of reference. As her therapist and as one who is older, he almost assumes the savior role that Nicole latched onto as a result of the incest with her father. Incest also contributes to how Nicole is never quite settled emotionally. She never establishes a fully functional emotional base from which her memories of incest can be put to rest. Dick's affairs and the mere intimation that he is unfaithful triggers emotional flights that are rooted from the abandonment of responsibility intrinsic to Devereaux Wilson's incestuous relationship with Nicole. She can never move far from the reach of what was done to her, just as the story is not able to stray far from the improper nature shown to be a part of incest. This same reach is evident in how Rosemary is infatuated with Dick and how they move into a relationship that borders on a similar plane of inappropriateness. It is not an accident that Rosemary found success in a film called "Daddy's Girl," helping to confirm the presence and reach of incest in the narrative.
Another function of incest is to display how some relationships are predicated upon superiority. The premise of incest is that someone is able to assert power over another. In this relationship, someone is dominant at the cost of another. Devereaux Wilson sexually dominates over his daughter, whose voice is silent. While incest is something to be condemned, Fitzgerald is quite skilled at showing how this dynamic of power and superiority functions in relationships. The beginning of the relationship between Dick and Nicole features him being powerful and her in a weakened and frail condition. As Dick's alcoholism begins to increase, the power dynamic shifts and she exerts the power that he once had. In leaving him and finding solace in Tommy, relationships are shown to be exercises where one holds power over another. When Devereaux comes back to Zurich and arranges for a moment to meet his daughter, power might be restored to Nicole. Yet, Devereaux escapes, incapable of being able to restore power back to one who lost it because of incest. In showing this dynamic, incest brings out a dimension of power, which, to a lesser extent, guides the premise of relationships in the narrative.