Torture, compassion, anger and romance
Kudos to kids who can read through this long, complex book. However, the anger and cruelty displayed in early chapters when one group of people terrorizes and tortures another group (including children) is quite disturbing. More terrorizing and violence follows at the end with characters dying, both from the 'good guy' and the 'bad guy' camps. And through the backstory of some new characters that is revealed, we begin to learn tragic details of what people did, turning against friends and family, during the evil Voldemort's rise to power.
The rest of the story line is similar to previous Harry Potter books, with the introduction of a few new themes. For the first time, good friends have a serious falling out, and have to work through resolving that. Characters begin to deal with romantic feelings. And a sudden awareness of inequalities and tensions between wizards and other magical races introduces a theme of political action and compassion.