By exploring the lineage of Tom Riddle—from his orphanage origins to his manipulation of Professor Slughorn—we learn that Voldemort is not a force of nature, but a product of choices. The concept of Horcruxes is introduced, shifting the goalposts of the series. The enemy is no longer a man to be defeated in a duel, but a soul to be dismantled.
The title itself is a masterclass in thematic parallel. While the world feared the rise of Lord Voldemort, Harry was inadvertently being guided by another "Prince"—Severus Snape. harry potter and the half-blood prince