Why is there an audience for a movie like “Obsessed”? Are people not aware of the Lifetime Movie Network, which shows films like this 24 hours a day for free?

Ah, but Lifetime movies don’t star Beyonce Knowles. This deprives viewers of the opportunity to see an R&B-pop diva call her husband’s admirer a “crazy b****” (which, in fairness, is putting it mildly) and bare her claws, literally and metaphorically, in a fight for her man. Oh, no, you didn’t! Aw, HELL no! Et cetera.

I confess the climactic cat fight in “Obsessed” is satisfying, partially on its own merits and partially because the story leading up to it has been so predictable and derivative that it’s nice to see something lively. Having an insane villain who is single-mindedly devoted to just one insane goal probably makes the screenplay easier to write: At all times, when contemplating what should happen next, you simply have her be as crazy as possible. But that’s not very interesting, is it?

There’s not a shred of nuance, depth, or backstory on Lisa Sheridan (Ali Larter), who comes to work at a high-rolling L.A. investment firm as a temp (“temp-TRESS,” assesses one of her horndog supervisors). She appears out of nowhere, succubus-like, as an efficient, businesslike, and beautiful office assistant, and immediately latches on to Derek Charles (Idris Elba), who is handsome, liked by everyone, and 100 percent devoted to his wife of three years, Sharon (Knowles).

Derek ignores Lisa’s advances, which is hard to do, since she is throwing herself at him like she’s a rug and he’s on fire. Sharon, for her part, is jealous of Lisa before she even has reason to be, simply because Lisa is gorgeous and works with her husband. I see this as a flaw in Sharon’s character, but the movie sees it as a positive thing. You go girl! And so forth.

Sharon has legitimate cause for concern soon enough, though. Derek refuses to do anything with Lisa, but that doesn’t stop Lisa from manufacturing a fictional relationship with him in her mind. At the office Christmas party — which for some reason spouses are not invited to, but temps are — Lisa corners Derek in the restroom, and now he knows she must be dealt with.

The screenplay, by David Loughery (“Star Trek V”), shuns subtlety in favor of pseudo-ominous lines like “I think you’ll find I’m not the typical temp” and idiocy like Derek’s co-worker (Jerry O’Connell) saying, “A lot of these single girls see the workplace as their hunting ground, and I think this one has you in her crosshairs.” (He follows this up by making a gun with his thumb and forefinger, aiming it at Derek, and saying, “Pshew!”) Derek’s regular secretary is a sassy gay fellow named Patrick (Matthew Humphreys) — gay because all TV and movie characters’ secretaries are sassy gays nowadays — and when Lisa offers to take him out for cocktails to catch up on office gossip, he says, “If you think you can pump me for information with a couple of cosmos — you’re right!” ARE YOU KIDDING ME, MOVIE??

My favorite, though, is when Derek comes home from work and is FINALLY going to tell Sharon about how Lisa has been harassing him, but before he can say anything Sharon says her sister’s husband just walked out on her after having an affair with a woman he worked with. And so Derek doesn’t say anything after all, because the situation is too similar and it would make Sharon furious.

As directed by Steve Shill (a widely experienced TV guy making his film debut), “Obsessed” isn’t campy enough to be cheesy fun, and it obviously isn’t smart enough to be legitimately entertaining, either. But it’s been shrewdly packaged. Casting Beyonce is good for $10 or $20 million at the box office by itself. Furthermore, it was a brilliant choice to make Lisa a white woman. If she and the other two main characters had all been black, the film would have been labeled a “black movie” and white audiences would have ignored it. Making her white eliminates that problem AND makes it more appealing to the black audience, because now it taps into the fear many African-American women have about white women taking all the good black guys. And if I was thinking about racial politics instead of paying attention to the movie, you can imagine how eager to wander my mind must have been.

Note: Contrary to regular industry practice, this film was not screened for critics before opening.

D+ (1 hr., 48 min.; PG-13, a little mild profanity, mild sexuality, some moderate violence.)