With “Trap,” writer/director M. Night Shyamalan has given us a half-decent movie. By which I mean that half of it is… decent. The first half delivers the taut thriller we’ve been promised, and it’s not great or anything, but it’s reasonably suspenseful and enjoyable. And then the movie becomes garbage. Not the unique, crazy garbage that only Shyamalan can deliver, but uncreative garbage that no self-respecting filmmaker wants to deliver.

At the beginning of the film, we are introduced to doting dad Cooper (Josh Hartnett). He’s taking his daughter Riley (Ariel Donoghue) to a concert by her favorite pop star, Lady Raven (Saleka Shyamalan). He learns from oversharing merchandise seller Jamie (Jonathan Langdon) that the FBI is monitoring the concert. They have a hot tip that a serial killer known as The Butcher is in the arena, and with the help of profiler Dr. Josephene Grant (Hayley Mills), they’re going to catch him.

This makes Cooper very worried. He starts behaving erratically and evasively, and it certainly looks like he’s The Butcher… because he is The Butcher. Don’t buy into any of those ridiculous fan theories about how, say, preteen daughter Riley is really The Butcher just because “the trailers ‘imply’ Cooper is The Butcher, but they don’t flat-out say it.” I’m flat-out saying it. The suspense in this movie comes from whether or not Cooper will be stopped or if he’ll kill anyone along the way. If you come into this movie expecting a mystery about The Butcher’s identity, you’ll be disappointed by more than just the weak second half.

The stuff about Cooper trying to weasel his way out of the arena really does work. The well-cast Hartnett is as engaging a lead as this movie could have, and Shyamalan expertly keeps the tension steadily growing. This being a Shyamalan film, it’s also important to note oddball supporting characters like Jamie and the mother (Marnie McPhail) of a girl that doesn’t get along with Riley. These characters effectively add to the suspense, and they’re completely unaware of it. I complained about these types of scene-stealers in my review of “Longlegs” a few weeks back, but this movie isn’t as obnoxious about trying to make everyone quirky.

The good times don’t last. Eventually the action leaves the arena and goes back to Cooper’s house, complete with wife Rachel (Alison Pill) and son Logan (Lachlan Miller). The perspective even shifts from Cooper to someone else for a little while. The venue change isn’t exactly where things start going downhill for this movie, but it’s soon after. The real turning point is when Cooper has to drop the façade and start behaving like a stereotypical bad guy. I was digging scared, desperate Cooper, but when he’s The Butcher, he’s neither scary nor interesting.

Then, of course, there’s that interminable ending. Cooper manages to fool the FBI more than once, which is all the FBI should be permitted. The agents are all dumb as bricks. Cooper should have just taken his chances with being questioned at the concert and he probably would have gotten away. He makes some annoying mistakes too, but I can somewhat chalk those up to mental instability. More problematic than the plausibility of the characters’ decisions is that the timing and energy are all off, like Shyamalan’s inspiration just ran out of gas. I guess he was so dead-set on getting the concert scenes right that he considered everything else expendable.

The pop music of Lady Raven is a good enough metaphor for “Trap.” It isn’t disastrous, like previous efforts from the Shyamalan family. I was relieved when Saleka proved to be a better singer and actress than her nepo-baby credentials would suggest. But at the same time, I couldn’t imagine any of these unmemorable songs becoming major hits. Just like I can’t picture “Trap” being anyone’s favorite thriller or Shyamalan movie. Here’s hoping you can easily get out of the theater.

Grade: C-

“Trap” is rated PG-13 for some violent content and brief strong language. Its running time is 105 minutes.

Contact Bob Garver at rrg251@nyu.edu.