Sexual tension
By placing high school boys and girls alone in private rooms at a house without parental supervision, the novel invites the theme of sexuality into the story, and much of the depictions of the characters depends on their sexual attractiveness or lack thereof, or of their relationships.
Imagery of death
The main imagery of the novel is the depiction of gruesome deaths. Many of the deaths are ironically connected to the character or some sort of perceived moral shortcoming.
Island imagery
The characters are on a private island partying like extravagantly wealthy people. This elevated status is part of what makes the murderer view the characters as immoral, since they are living lavish while other people suffer. Therefore, the novel contains imagery of partying and island life.
Darkness
Because darkness affords opportunity for bad things to happen, much of the scenes include shadow, night, and various other expressions of darkness. This also helps to set the mood and tone for the novel, which is horrific.
