In one way, Ten is about psychological horror, vengeance, and the unspeakable sadness of life. But, since its characters are all adolescent, the best interpretation would be that the book is expressing those basic ideas from the horror genre through transforming characters who are forced to become adults in light of the trauma and danger of their situation.
This novel could be a reflection of the tragic occurance of school shootings and the way those events leave the community wondering what could have been done, wondering why they didn't understand the severity of the situation until it was too late. Indeed, those are the basic concerns of the story.
The integral inclusion of mental health as a subject of discussion in the book is also very meaningful, since it helps to reframe the events of the plot in a way the reader can understand—for the first time in most of their lives, the teenagers are experiencing true fear and true regret, and this experience is driving them into traumatic mental states. So this book is also a depiction of the way that mental illnesses develop during puberty (since they commonly do arise during puberty).
Overall, the novel is about tragedy, the horror of life, and the sadness and injustice of those people like the murderer whose morality becomes corrupted by suffering.
