Harry Potter and the Half-Blood Prince
Dumbledore works closely with Harry to prepare him for the final battle with Voldemort. Dumbledore teaches Harry about Voldemort's past, and Harry becomes an expert in Potions, thanks to tips written in the textbook by the mysterious half-blood prince. As they pursue Voldemort, Dumbledore is murdered. Harry, Ron, and Hermione seek revenge and the ultimate defeat of Voldemort.