Diving into the sea of summer cinema, amidst dueling robots, a flamboyant fashionista and tired retreads of animated prehistoric critters, comes yet another blockbuster hopeful.

But — gasp — it seems it’s a blockbuster dependent not on explosions or outrageousness, but on the previously thought missing link in most of this summer’s films — a story.

Delayed from a November release, “Harry Potter and the Half-Blood Prince” is a well-paced, quietly assured film with pockets of action and humor tucked in all the right places. The end result is a two-and-a-half-hour movie that earns its keep for every one of those minutes.

This time, Harry (Daniel Radcliffe) is back for his sixth year at Hogwarts. Meanwhile, havoc is being wreaked all over the place thanks to the Death Eaters, and it seems as if nowhere — even Hogwarts — is safe.

At the school, Albus Dumbledore (Michael Gambon) enlists Harry to help find out more about Voldemort’s defenses via Professor Horace Slughorn (Jim Broadbent), a former potions professor who Dumbledore convinces to teach again. Slughorn taught Voldemort years ago, and holds vital information.

While in Slughorn’s class, Harry finds an old textbook filled with helpful spells that belonged to someone called the Half-Blood Prince.

Romance is also in the air as Hermione (Emma Watson) struggles with her feelings for Ron (Rupert Grint) while he pursues another girl, and Harry falls for Ron’s sister Ginny (Bonnie Wright).

“Half-Blood Prince” manages to combine all kinds of atmospheres convincingly — it’s filled with both a deepening sense of dread and an optimistically strengthening sense of relationship among the major characters. Radcliffe, Watson and Grint have all come into their own, and their rapport is strong and believable throughout the film.

Director David Yates, who also helmed the previous Potter film, “Order of the Phoenix,” and will direct the upcoming two-part finale, “Deathly Hallows,” has crafted a dark and increasingly mature entry into the franchise.

Frightening touches like a cursed girl screaming while suspended in mid-air and an underground lake teeming with Gollum-like villains defy the PG rating that “Half-Blood Prince” somehow snagged from that most inexplicable of institutions, the MPAA.

Yates populates the magical world with lots of nice detailed touches as well, including imaginative renderings of an hourglass that keeps time based on the quality of the conversation around it, and vials of memories that can be visualized by pouring them into a shallow pool.

Any idea that “Harry Potter” is mostly kids’ stuff should be dispensed of with this film — evil persistently wins in this outing, and the ending is undeniably downbeat as things are set up for the big finish. Bad guys Severus Snape (Alan Rickman), Draco Malfoy (Tom Felton) and Death Eater Bellatrix Lestrange (Helena Bonham Carter) are the ones who triumph.

“Half-Blood Prince” does exactly what a film of its kind ought to — cast an engrossing spell on its audience. Movie fans with a fetish for non-stop action might be disappointed, but perhaps it’s time these people were introduced to a different kind of movie magic — a slowly unfolding dialogue-driven story. On this front, “Half-Blood Prince” delivers.

4 out of 5 Stars

-Dusty Somers is the Life & Arts editor and a journalism junior.