The Half-Blood Prince (Rowling, 2005)

The answer for the identity of Half-Blood Prince leads readers to the key theme, and the tension between stratification by expertise and classification by lineage. Harry borrows a textbook for potion making. The book is scribbled with various tips on potion making and spells that help Harry to complete his tasks in potions class. To Harry’s surprise, Snape becomes the professor for the Defense against Dark Arts course. Dumbledore provides Harry with independent study which is composed of tracing back the memories about Tom Riddle, who later becomes Lord Voldemort. Draco Malfoy’s mother asks Snape to protect her son, Draco Malfoy who is ordered by Voldemort to kill Dumbledore. Snape agrees to do the job himself. Draco attempts to assassinate Dumbledore and suffers the horror of his own death in case he fails to complete the mission.
Harry accompanies Dumbledore to destroy a horcrux among seven horcruxes which carry the divided souls of Voldemort who desires immortality. Dumbledore explains to Harry about the production of Horcruxes: Tom Riddle’s diary, Marvolo Gaunt’s [Voldemort’s grandfather] Ring, Helga Hufflepuff’s Cup, Salazar Syntherin’s Locket, Rowena Ravenclaw’s Diadem, Harry Potter and Nagini [Voldemort’s beloved snake]. Dumbledore becomes weak as a result of his injury while destroying another horcrux, Marvolo Gaunt’s ring, which attacks its wearer to death and Salazar Slytherin’s Locket which requires Dumbledore to drink potions that cause him pain, despair and hopelessness.
At the end the book, Death Eaters attack Hogwarts. Snape kills Dumbledore and only Harry witnesses this. Frustrated and furious with the death of Dumbledore, Harry attacks Snape with lethal curses. Snape discloses that he is the Half-Blood Prince who creates charms and potions that Harry takes advantage of. Hogwarts loses its headmaster and security. Students leave Hogwarts. Instead of returning to Hogwarts, Harry decides to search for the rest of the horcruxes to destroy them and in turn, destroy Lord Voldemort. Ron and Hermione announce to accompany Harry’s quest.