The unknown murderer
To a normal, healthy person, the reality of serial killers should be disturbing and confusing, as it was for the teens in the story. The likelihood of someone commiting not just one but many acts of violence to this gruesome extent seems impossible, but unfortunately, it does happen, as the characters learn. An interesting way to interpret the book is that it provides a commentary for the terror of school shootings.
The murder party
This story is like a Murder Mystery party, but with real (fictional) murders. Basically, the juxtaposition of the party and the lavish island life is ironic when coupled with the horror and terror of serial murder.
The plot twist
When the plot twist is finally revealed, it's terrifying and surprising all at once. The unlikely scenario is so nightmarish and twisted that the reader is left feeling pity for the murderer, because ironically, it's easy to see what drove that person crazy—the sadness of a sister's suicide.
The eros of the story
One might not expect a horrific story like this one to include sexuality as a theme, but like many others in the horror genre, sexuality is actually right at the center of the story, both concretely and abstractly.
The horror and beauty of life
There is a reality which the characters in this story must face: In light of their blooming sexualities, they must realize the true gravity of their choices. That doesn't mean that the murderer is on the side of justice, but it does mean that the young adults must recognize that their decisions have 'life or death' implications.
