Between the darker tone and heavier themes of Order of the Phoenix and the all-out epic conclusion to the series in Deathly Hallows, it’s easy to overlook Harry Potter and the Half-Blood Prince. It seems lighter, softer, tamer, and far less significant. The movie was rated PG, while all the others from Goblet of Fire onward were PG-13. Its plot spends a great deal of time focusing on teenage romantic drama and day-to-day life at Hogwarts, while Voldemort himself never appears except in flashbacks and in the looming threat of danger that remains in the background until the end. It’s certainly not the most exciting Harry Potter book, and I’ll admit it’s not my personal favorite. But it does have a significant role to play.
Order of the Phoenix is about loss of innocence. Not that Harry has ever been totally innocent, at least not in the “sheltered and naïve” sense of the word. But in Order of the Phoenix, he has seen his parents’ killer return from the dead and murder one of his classmates, barely escaped with his own life, and attempted to warn his fellow wizards, only to be mocked, ridiculed, and viewed as either delusional or a liar by almost everyone. He sees the most trusted adults in his life fighting in secret to protect the wizarding world from a threat it won’t acknowledge exists, and at school, he does the same with his friends, forming a Defense Against the Dark Arts study group that grows into a full-blown resistance movement. Meanwhile, his dreams are haunted by that night in the graveyard and by visions of what Voldemort is doing, leading him and his friends into a battle against the Death Eaters where Harry loses one of his father figures and has to withstand being possessed by Voldemort. Harry has certainly endued hardships before, but this is different.
Order of the Phoenix is about loss of innocence, and Deathly Hallows is a high-stakes war story. In contrast, Half-Blood Prince is a last chance for Harry and his friends to just be teenagers. The world believes them now; the adults in power are doing their best to defeat Voldemort; Harry has heard the prophecy and knows he will have to face him someday, but that might be years in the future; and in the meantime, he has tests to pass, Quidditch games to win, and a growing crush on Ginny to deal with.
That doesn’t mean it’s filler, though. I would argue that Harry needs the chance to be a teenager before he sets off on his quest to defeat Voldemort. He needs to understand and experience the normal life he’s giving up in order to be the Chosen One. More importantly, he’s fighting to allow others – perhaps not his classmates, who mostly get drawn into the war along with him, but the younger students and the next generation – to live in a safer world where they will be able to live normal lives, and where teenagers will not have to fight in wars against Dark Wizards. Those moments “out of someone else’s life” that he spends with Ginny matter more than they seem to at first. Ron, Hermione, and to an extent all the children of Hogwarts are also given one last peaceful year before the full-fledged war portrayed in Deathly Hallows.
I said that Order of the Phoenix is a loss-of-innocence story, but so is Half-Blood Prince – not for Harry himself, but for Draco Malfoy. Like Harry, Malfoy has never been entirely innocent – he’s a vicious, mean-spirited bully – but in his own way, he’s incredibly sheltered and naïve. He doesn’t seem to have had an independent thought in his life and has never been through any real hardship. In Half-Blood Prince, he’s recruited to work for Voldemort and given a special mission to kill Dumbledore, which does not go according to plan. He becomes increasingly sullen and withdrawn as the year goes on, before finding himself unable to commit murder when the opportunity finally arises. In the same way that Harry transformed from child hero to pariah to resistance leader, Draco goes from playground bully to Death Eater to a conflicted young man incapable of either true good or true evil. Their stories are parallels that come to opposite conclusions, which makes sense since they are foil characters.
Finally, Half-Blood Prince sets the stage for Deathly Hallows. In Harry’s private lessons with Dumbledore, they explore flashback memories of Voldemort’s past, which allow them to figure out what kind of Dark Magic he used to make himself immortal and how to reverse it. His journey in Deathly Hallows revolves mostly around this, ending with the revelation that Harry himself must die in order for Voldemort to die – and, of course, the further twist that he doesn’t die at all. Dumbledore’s death at the end puts Harry in a position of having to face Voldemort alone, without his most powerful protector, while Snape’s actions seem to establish his role as a villain rather than an ambiguous character in Deathly Hallows, thus subtly setting the stage for the revelation of his true loyalty.
While the threat of Voldemort is present only in the background, it’s still there, and it casts its shadow over the whole story. Students are pulled out of school by parents who are afraid the school is not safe. Shops in Diagon Alley close down when the shop owners go missing. Bridges mysteriously collapse, morally-lacking opportunists sell bogus protective charms, and thanks to Polyjuice Potion and the Imperius Curse, you can never be quite sure who might not be who they seem. The war against Voldemort is raging in the background, a student is plotting to kill the Headmaster, Harry is learning and preparing to eventually fulfill the prophecy, and by the end it’s clear that he will have to do so sooner rather than later. All of this leads directly into Deathly Hallows, which in turn builds up to the Battle of Hogwarts and the final confrontation between Harry and Voldemort.