It begins with two women sitting quietly on a bench in New York City's Central Park.

Above the din of traffic noise and the rising wind, a scream.

"Did you hear that?" the first woman asks her friend. She looks down the avenue.

"Are those people clawing at themselves? Is that blood?"

We never see any of this, yet our heartbeat slams into overdrive, our imaginations race, and the question becomes a battering ram that smashes into our brains over and over: What's happening? What's happening?

I'll tell you what's happening: M. Night Shyamalan has done it again!

He's created another spooky, weird and eerie thriller that starts out mysterious and foreboding, then quickly falls off the cliff of credibility with a disappointingly weenie finale.

The entire opening sequence of "The Happening" demonstrates writer/director Shyamalan at his best, up there with "The Sixth Sense" and most of "Signs." (Because I judge "Unbreakable" to be only the first act of a bigger movie that Shyamalan never made, it's not his best work.)

No surprises will be spoiled here, but if you've seen the TV commercials and trailers for "The Happening," you already know that people jump from high-rise buildings and something unseen and deadly sweeps through the country, causing panicked people to flee from New York and Philadelphia, only to discover they have not eluded the danger.

Like Shyamalan's critically excoriated "The Village" and his strange, unengrossing follow-up, "Lady in the Water," "The Happening" soars or crashes on the strength and imagination of the answer to that pounding question, "What's going on?" Although Shyamalan deserves credit for being imaginative - and tossing in a vaguely pro environmental message along the way - his answer to "What's happening?" feels dissatisfying and unworthy of his superbly macabre setup.

It doesn't help that his above-the-title main star Mark Wahlberg has less facial expressions than a stoned Chuck Norris.

Wahlberg plays Elliot Moore, a Philadelphia high-school science teacher afflicted with what appears to be a permanent case of constipation, judging by his perpetually furrowed brow and pained grimace. He also obsesses over his mood ring that tells if someone's "romantic" or "peaceful," but apparently doesn't have a color signifying "scared poopless."

As news of a terrorist bio-attack in New York reaches Philly, Elliot high-tails it out of town with his oddly distant wife Alma (Zooey Deschanel), his math teacher best friend Julian (John Leguizamo) and Julian's withdrawn 8-year-old daughter Jess (Ashlyn Sanchez). Julian says his never-seen wife will take the next train out. Yep, it's like the guy who says "I'll be right back" in a mad slasher epic.

None of these characters proves to be particularly interesting. The overt marital conflict threatening to break up Elliot and Alma turns out to be a ripple in a teapot: She feels guilty she lied to her husband the night she went out and shared a dessert with a co-worker!

Shyamalan turns your average high school science teacher into a heroic action figure with a brain as well as a survival instinct. Elliot's knowledge of basic science comes into play during a key scene where he puts the puzzle pieces together and comes up with the only logical explanation for the outbreak of death and insanity. A subdivision billboard with the phrase "You deserve this!" provides an ironic clue to the mystery.

"The Happening" never loses its ability to creep us out, even near the end when the Moores and little Jess come across an isolated farmhouse that might be run by a distant relative (Broadway star Betty Buckley) of the Norman Bates family. James Newton Howard deserves credit for augmenting the nervous edge with his subtle, tingling string score.

Nonetheless, if I'd been wearing Elliot's mood ring during the finale of "The Happening," it certainly would have turned the color of disappointment.

"The Happening"

Rating: 2½ stars

Starring: Mark Wahlberg, Zooey Deschanel and John Leguizamo

Directed by: M. Night Shyamalan.

Other: A 20th Century Fox release. Rated R (violence). 90 minutes.