In "Harry Potter and the Half-Blood Prince," the sixth book in the Harry Potter series by J.K. Rowling, Harry Potter returns to Hogwarts School of Witchcraft and Wizardry for his sixth year. He learns more about Lord Voldemort's past through private lessons with Professor Dumbledore, uncovering the dark wizard's origins and the concept of Horcruxes, objects containing pieces of his soul. As the story unfolds, Harry discovers a mysterious textbook belonging to the Half-Blood Prince, which helps him excel in Potions class. Meanwhile, the wizarding world faces increasing danger from Death Eaters, leading to significant events that set the stage for the final confrontation in the series.