PG-13 movies, at most, get one F-bomb, and “Breaking In” spends its single use of the word well. In the finale, the film’s star, Gabrielle Union, drops the solo **** at just the right moment for maximum, crowd-pleasing impact. There will be applause.

The moment encapsulates the appeal of this bare-bones, so-so home-invasion thriller: Gabrielle Union getting to be awesome.

At 45, the Omaha native has already had a long entertainment career, landing small roles in bigger films like “Bad Boys II” and big roles on smaller screens (“Becoming Mary Jane”). She’s starred in ensembles (“Think Like a Man”), and she’s played second fiddle (“Bring It On”), but she’s rarely had so much of a movie as “Breaking In.”

It’s the first feature film in which she’s the sole name above the title. Also serving as producer, Union is in nearly every shot of her new movie: running, jumping, punching, stabbing and dropping that judicious F-bomb. She handles herself so capably and delivers her performance so ferociously that this should kick open the door for her action-hero rebrand. It’s just a shame the movie around her isn’t all that good.

At its best, “Breaking In” is a B-team “Panic Room,” a tiny thriller with an elegantly spare premise that doesn’t know how to rise above the baseline of its genre.

The film is, at least, dirt-simple. Union plays Shaun, whose father has just been killed in a hit-and-run, leaving her with a large country house to deal with. Shaun takes her teenage daughter and her younger son to the house for the weekend, planning to pack up a few things before she puts the home on the market. She just happened to pick the wrong weekend.

Almost immediately, four thieves — led by a dead-eyed sociopath played by Billy Burke — break into the house. They’re looking for a safe with $4 million in it. The burglars find and bind the children, trapping Shaun outside of the house (without her cellphone). She wants to get in and save her kids, but her dear old dad was a paranoid sort, and before he died he turned his home into a giant fortress, a house-sized panic room with retractable polycarbonate shields on the windows and security cameras circling the perimeter. Shaun has to get creative if she’s going to break in.

That’s it. That’s the movie. A premise this simple can work, but the script and visuals have to be really inventive; they have to vary the setpieces enough to keep the scenes from growing monotonous and sapping the movie of momentum. The 2016 thrillers “Hush” and “Don’t Breathe” are great examples of how to do this sort of thing. But “Breaking In” is, by comparison, visually flat and sluggishly paced. The film rallies a bit in its final stretch as Union brings the fight to the intruders, but director James McTeigue and screenwriter Ryan Engle struggle to give this cat-and-mouse game any definable shape. After a while, everyone’s just spinning around in circles waiting for the movie to run out of road.

Despite all this, the movie still might be worth seeing for the performance by Union. (If you’re an Omahan, it’s your civic duty to go see her on the big screen this weekend.) And there’s a thread of female empowerment running through the film that’s undeniably rousing whenever “Breaking In” bothers to tug on it.

With her kids held captive, Union listens while Burke’s burglar dares her and, in turn, dooms himself: “There’s nothing you can do,” he tells her. “You’re a woman. Alone and at the mercy of strangers.”

Watching Union rise to that challenge, her face shifting from helpless terror to steely resolve, is the film’s great pleasure. Hopefully, Union’s spark of righteous rage can be put to further use in better films to come.