School Year:
* Dumbledore's Army: Harry and Dumbledore recruit students to learn defensive spells, preparing for the impending war against Voldemort.
* The Half-Blood Prince's Potions Book: Harry discovers an old, annotated copy of the Potions textbook with insightful notes and spells, seemingly by a skilled and powerful wizard.
* Romance and Tragedy: Harry develops feelings for Ginny Weasley, and Ron struggles with his own romantic pursuits. Tragedy strikes as Dumbledore's former student, Katie Bell, is poisoned by a cursed necklace.
* The Death Eaters' Attacks: Voldemort's forces become more active, attacking Hogwarts and the Muggle world.
* The Secret of the Half-Blood Prince: Harry investigates the book's mysterious owner and discovers his identity as Tom Riddle, a young Voldemort.
Dumbledore's Mission:
* The Horcruxes: Dumbledore reveals Voldemort's secret: he split his soul into Horcruxes to achieve immortality. They embark on a quest to find and destroy them.
* Memories and the Past: Dumbledore shares memories of his own past with Harry, including his friendship with Tom Riddle and the tragic downfall of his beloved, Ariana.
* The Cave and the Horcrux: Dumbledore and Harry journey to a secret cave to retrieve a Horcrux, a locket, but their mission is fraught with danger and sacrifice.
The Climax:
* Dumbledore's Death: The cave experience leaves Dumbledore weakened and vulnerable. He is fatally injured by Severus Snape, who is revealed to be a Death Eater.
* Snape's Betrayal: Snape reveals his true intentions, claiming to have always served Voldemort and killing Dumbledore for his own gain.
Aftermath:
* Voldemort's Reign: With Dumbledore gone, Voldemort consolidates his power and seizes control of the Ministry of Magic.
* Harry's Isolation: Harry grapples with grief and disillusionment, struggling to understand the events and the implications for the future.
* The Legacy of the Half-Blood Prince: Harry is left with the responsibility of finishing Dumbledore's mission and uncovering the secrets of the Half-Blood Prince.
These major events set the stage for the final battle in Harry Potter and the Deathly Hallows.