As Harry and company return to Hogwarts, things have changed. The threat that Voldemort poses is much more immediate. The students are constantly getting news of people that have ‘disappeared’, some of them relatives of Hogwarts students. And there is fear that despite all of its defenses, Hogwarts may not be impervious to attacks by Voldemort and his Death Eaters.
In potions class, Harry gets a used textbook with notes, shortcuts, and spells scribbled in the margins by its previous owner, the Half-Blood Prince. (Ladies and gentlemen, we have a title.) These spells appear to be of the prince’s own creation, and some of them involve darker magic than Harry is used to.
With the help of Dumbledore, Harry begins to find out pertinent information about Voldemort’s past. Horcruxes, y’all! Horcruxes. I am glad that I don’t have to wait for a year to read the next one.