What is a good theme for this novel?

Morality and ethics are central to the messages in The Kill Order. The first day of the story, government officials shoot poisoned darts at its remaining "citizens." This is not moral, and yet the people who committed the atrocity have their own reasons for doing so. Furthermore, there are several mercy killings in the story: friends are forced to put their friends out of misery, so that they will not keep suffering. The question of killing people is brought out into the light, and what role morality has to play in that. Mark constantly asks himself what is right and what is permissible in this mess of a world.