A dark and powerful force has crept into the Hogwarts School of Witchcraft and Wizardry. Its looming presence has been hinted at before, but now it is here, an implacable fact of life. Strange and beguiling metamorphoses are in store for boy wizard Harry Potter (Daniel Radcliffe), his loyal comrade Ron (Rupert Grint), and their plucky pal Hermione (Emma Watson). This subtle demon has a name, terrible to pronounce. Beware … Puberty!

The fire, in “Harry Potter and the Goblet of Fire,” is in everyone’s pants. Harry is growing into a nerd-chic hottie who enjoys lounging topless in bathtubs haunted by flirtatious female ghosts. Ron’s getting randy, which might be fueling the fire of an adolescent (and homoerotic?) rivalry with his spell-casting confrere. And Hermione, flush with hormones, finds herself atremble for Viktor Krum (Stanislav Ianevski), a ripped Euro gymnast-mage several years her elder.

Yummy Krum is on the scene to participate in the Triwizard Tournament, a grand contest pitting the brightest pupils from the best magic schools against one another in a series of dangerous tests. Flanked by his fellow Durmstrangians, who resemble nothing so much as the studs in a Budapest porn flick, Viktor makes a flaming, knee-weakening entrance. Watch out, kids, it’s getting PG-13 up in here.

Also participating in the Triwizard are the Beaubaton beauties, led by the delightfully developed Fleur Delacour (Clemence Poesy). On their entrance to Hogwarts, special attention is given to the sway of their synchronized bottoms, a rather startling sign of the newly sexed-up Harry Potter saga.

We may credit that naughty peek to Mike Newell, the latest director to take over the reins of the blockbuster franchise. A maker of romantic comedies (“Four Weddings and a Funeral”) and middling chick flicks (“Enchanted April,” “Mona Lisa Smile”), Mr. Newell sounds like just the man for a Potter film with a prom sequence. After all, this is a fantasy in which the magic moments sometimes involve teleportation and levitating spiders, but more often result from the enchantments of teenage love.

Mr. Newell does improve on the snooze-en-scene of the first two Potters by “Home Alone” hack Chris Columbus – which isn’t saying much. His sense of comic timing has been crushed by the bulk of a megaproduction. His characterizations are either muted or hysteric. The film has no discernable rhythm; he sustains a bland, blob-like, middlebrow know-how.

This flat-footedness, whether of the actors or CGI set pieces, is an acute letdown after the swift, focused intelligence Alfonso Cuaron brought to the most recent entry. There may yet be another Potter film as stylish and satisfying as “The Prisoner of Azkaban,” so long as the moneymen take a chance on another quasi-outsider auteur. (It had to be the risque “Y Tu Mama Tambien,” not his safer forays into studio pictures that got him the gig.)

Where “Azkaban” was one of last year’s most enjoyable film fantasies, “Goblet” is obligatory for the Potter cult but no one else. As the fourth of seven Potter films, it’s something of a hesitant, unremarkable middle child. If you haven’t read the books or kept up with the first three films, if you draw a blank at the words Quidditch, Dumbledore, and Voldemort, forget about it. If you’re among the many millions who have kept up, you may yet wonder at the lack of dramatic momentum, how little excitement pours over from six-plus hours of the Potter saga into this very weighty (157 minutes!) “Goblet.”

Guess what? Potter is once more plagued by dark portents and enigmatic anxieties.The fate of our beloved crypto-ubermensch continues to unfold as he draws closer to evil Lord Voldemort (a freakishly noseless Ralph Fiennes), slayer of Potter’s parents. For his part, Mr. Radcliffe is once more plagued by a lack of charisma, emotional texture, and superheroic heft. Sure, he can shoot hoodoo voodoo out of his magic wand, but how about conjuring a performance? Maybe they teach that at Gandalf Graduate School.

It’s always a pleasure to watch Michael Gambon’s gentle Headmaster Dumbledore, Maggie Smith’s strict Minerva McGonagall, and Alan Rickman’s dependably hilarious Severus Snape, though each of them recedes, regrettably, to the background of the plot. More attention is paid to the latest, and hammiest, additions to the cast: Miranda Richardson as the ridiculous journalist Rita Skeeter, and Brendan Gleeson as Mad-Eye Moody, a visiting professor of Defense Against the Dark Arts.

The latter proves seminal to Harry’s success in the Triwizard Tournament, helping him in various ways to wrest his golden egg from a dragon, survive an underwater ordeal, and make his way through a topiary labyrinth to snatch the Goblet of Fire. Mad-Eye is not what he seems to be, which will come as no surprise to those familiar with the increasingly predictable and tedious pattern of the tale. “Goblet” isn’t the worst way to kill time at the multiplex until “King Kong,” fingers crossed, smashes it to smithereens. What disappoints is how little feels at stake. This vast multipart epic asks us to care about a young man’s coming of age, but hasn’t bothered to make him an intelligible hero, or even a mildly interesting one. Every time he gets one of those metaphysical migraines I wish Dumbledore would just break out the magic Advil.