In Harry Potter and the Half-Blood Prince, the protagonists, who are in their sixth year, have passed their OWLs and start on their specialist NEWT courses. Voldemort is leading another wizarding war, which has become so violent that even Muggles have noticed some of its effects. Although Harry and friends are relatively protected from that danger at Hogwarts, they are subject to all the difficulties of adolescence. At the beginning of the novel, he stumbles upon an old potions textbook filled with annotations and recommendations signed by a mysterious writer, the Half-Blood Prince.