“You need a shave,” says Albus Dumbledore (Michael Gambon) to Harry Potter (Daniel Radcliffe) during a scene in Harry Potter and the Half-Blood Prince — and damned if there isn’t a trace of stubble shadowing the lad’s chin. And there’s a pitch-perfect tone to Gambon’s delivery — not chiding, but with an almost wistful disbelief that this could be the same pink-cheeked boy who was plucked six years earlier from a cupboard under the stairs and thrust into the middle of a magical civil war.

Eight years and six films into the Harry Potter series, it’s undeniable that a lot of the pleasure in the latest installment is a result of the experience of watching children become young men and women before our eyes. J. K. Rowling’s books created a witty, magnificent mythology, but at their core they were always fundamentally about growing up. Harry Potter and the Half-Blood Prince shows the films continuing to mature just as its protagonists are, with all the humor, awkwardness, and heartbreak that such a journey entails.

The Death Eaters are still on the march as a new school year begins at Hogwart’s, and everyone seems to have a secret agenda. Dumbledore cajoles retired instructor Horace Slughorn (Jim Broadbent) back to work at Hogwart’s for an unknown purpose. Draco Malfoy (Tom Felton) has been recruited into a secret mission by the other servants of Voldemort, including Bellatrix Lestrange (Helena Bonham Carter). Even Harry’s frayed copy of his potions textbook presents a mystery, with its copious marginalia attributed to “The Half-Blood Prince.” Everyone would seem to have quite a lot on his or her plate simply trying to stay alive.

However, these are 16-year-olds we’re talking about, and as such, they tend to have their minds on other things. Screenwriter Steve Kloves spends a lot of time on the characters’ burgeoning romances, as Hermione (Emma Watson) fends off the advances of self-absorbed Cormac McLaggen (Freddie Stroma) while fretting over seeing Ron (Rupert Grint) find a girlfriend. Harry, meanwhile, gets all twitterpated over Ron’s younger sister Ginny (Bonnie Wright). Director David Yates — returning from Order of the Phoenix — effectively guides his young cast through tricky territory, making their frustrated fumblings as endearing as they are uncomfortable to watch.

And it continues to be a delight following the three lead actors as they grow into their roles — and play off one another so naturally. Only-children Harry and Hermione spar like a brother and sister neither one ever had, becoming confidantes when both are low, while Ron’s good-natured obliviousness provides the ideal comic-relief fulcrum. It’s a pleasure, too, visiting again with Hagrid (Robbie Coltrane), McGonagall (Maggie Smith), and Snape (Alan Rickman) — even as newcomer Broadbent continues the tradition of Hogwart’s guest faculty stealing the show — but the central trio hold their own. There’s so much goodwill built into their interactions that a smart filmmaker probably needs simply to get out of the way.

There is, of course, always the problem of condensing Rowling’s story. In the first two films, Kloves seemed too concerned with packing in plot details for the books’ fans, but like the series itself, he has relaxed and grown. Half-Blood Prince is far less dense with magical action than its predecessors, and perhaps that makes it feel mostly like a stage-setter for the finale that will be Deathly Hallows. Yet it’s so rich with characterization that it scarcely matters.

Hardcore Potter-ites know, of course, that Half-Blood Prince concludes with a spoileriffic plot development, and in fairness to those few who remain unaware, it’s best not to name it. But even the way the film builds to that moment shows how keenly Kloves and Yates are aware that it fits into Harry’s maturation into manhood.

This is a dark and foreboding tale, filled with plenty of disturbing images — including the hexing of a young student that plays like a demonic possession and an attack by a swarm of creatures a bit too reminiscent of Lord of the Rings‘ Gollum — that make the switch back from Goblet of Fire and Order of the Phoenix‘s PG-13 to PG seem as arbitrary as it is befuddling. Harry Potter’s story at this point isn’t one for children — nor is it a story about children. Not anymore.