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. While the shortcuts written in the book help Harry to excel at potions, he eventually learns to mistrust the anonymous writer's spells. Harry also takes private tutoring with Albus Dumbledore, who shows him various memories concerning the early life of Voldemort. These reveal that Voldemort's soul is splintered into a series of horcruxes, evil enchanted items hidden in various locations. Harry's snobbish adversary, Draco Malfoy, attempts to attack Dumbledore, and the book culminates in the killing of Dumbledore by Professor Snape.
Harry Potter and the Deathly Hallows, the last book in the series, begins directly after the events of the sixth book. Voldemort has completed his ascension to power and gains control of the Ministry of Magic. Harry, Ron, and Hermione drop out of school so that they can find and destroy Voldemort's remaining horcruxes. To ensure their own safety as well as that of their family and friends, they are forced to isolate themselves. As they search for the horcruxes, the trio learn details about Dumbledore's past, as well as Snape's true motives.
The book culminates in the Battle of Hogwarts. Harry, Ron, and Hermione, in conjunction with members of the Order of the Phoenix and many of the teachers and students, defend Hogwarts from Voldemort, his Death Eaters, and various magical creatures. Several major characters are killed in the first wave of the battle and Voldemort resumes his intention to kill Harry. In an effort to save the survivors, Harry surrenders himself but the battle resumes as the parents of many Hogwarts students, residents of the nearby village Hogsmeade and other magical creatures arrive to reinforce the Order of the Phoenix. With the last horcrux destroyed, Harry finally faces Voldemort. Harry offers the Dark Lord a chance at remorse, but Voldemort ignores this and attempts to kill Harry one final time; resulting in Voldemort's death, again, by a rebounding spell (the complications of which are described in depth near the end of the novel). An epilogue describes the lives of the surviving characters and the effects on the wizarding world.
