The novel explores darkness as a physical and spiritual motif. Charles and Cal have dark skin, dark hair, dark eyes, and a dark aura. Their darkness emphasizes the lightness of their blond brothers—and vice versa. Characters seem automatically attracted to Adam and Aron but immediately put off by the darkness of Cal and Charles. This prejudice stems from the mark of Cain in the Bible, which Charles obviously has in the form of a dark scar on his forehead. Cain’s punishment after killing Abel is to walk the Earth a scarred man. The dark mark on Cain’s forehead will pass down through the generations, marking all his descendants as sinful. Charles and Cal’s physical darkness becomes almost a self-fulfilling prophecy. Because they’re treated as plausibly bad and unattractive, they lean into that identity and act bad. Their spiritual darkness links to their physicality—and to the love withheld from them because of their dark exterior.

The novel follows two sets of brothers, the second pair of which parallels the first pair. The half-brothers Adam and Charles are close in age, and their conflicts center around Charles’s violent temperament, for which the trigger is his jealousy and resentment that their father loves Adam more, even though Adam does nothing to deserve that love.