“The Old Woman with the Knife” is a Korean variation on the World of Assassins tale, where killing for hire is a business with professionals assigned out of offices and following “rules.” It’s another story of an aged killer competing with a younger one to see who gets whom first.

And yes, we’ve seen versions of this where all the killing is done with knifes, poison and garrotes until somebody — usually mobster victims — figures out that pistols are a decent defense against such cutlery “artists.” The third act becomes bullet-riddled just as arbitrarily as the first two acts were sliced and diced.

Veteran Korean actress Lee Hye-yeong (“The Devil’s Game”) stars as the assassin her employer calls “Godmother” in her advanced years, but who used to be nicknamed “Nails” and took on the name “Hornclaw” because that’s how she rolls.

But way back in ’75, she was a battered young woman (Shin Si-ah) taken in by a mop-topped diner owner, Ryu (Kim Mu-yeol) and his wife. His work takes him away from home for days at a time. One homecoming, he arrives to find that their new dishwasher has fought off and killed a rape-minded thug of a U.S. G.I.

It turns out Ryu’s “pest control” work is killing human pests. He treats it as a calling. But as crime victims and the bullied start paying for “pest” removal, the Sinseong Agency goes professional, “eliminating malignant vermin” from society. Hornclaw has found her destiny.

Decades later, Ryu’s long gone but Godmother Hornclaw is still the best if you need a brutal bookie poisoned on the subway or some other “pest” out of your life. But she’s going soft. That injured, abandoned and aged dog she finds demands her pity.

“It’s awful to be abandoned when you’re old and sick,” the kind veterinarian (Yeon Woo-jin) tells her, in Korean with English subtitles. So she takes in the dog.

The punk who goes by Bullfight (Kim Sung-cheol) is a freelancer who has to be talked into joining an agency where he’ll get paid for the killing that seems to come naturally to him. “Nails” isn’t as hard as she used to be, with joint pains and eye problems and the agency’s doctor refusing to hide that from her boss. Bullfight will act as “backup” on her tougher jobs.

We’ve all seen “The Mechanic,” “John Wick” and a DVR full of old-killer/young killer tales. We know how this “relationship” will play out. And we fear for the dog.

Director and co-writer Min Kyo-dong goes back to 1999’s “Memento Mori,” so he does what he can to make this formulaic script (based on Gu Byeong-mo’s novel) surprising. There are several twists to hold our interest over 125 minutes. OK, maybe for 90 minutes of that.

Lee is a somber presence at the center of this, handling the fight choreography (as if anybody believes a 65 year-old woman could kick this much ass) and rarely betraying emotions, an unsentimental killer who gets sentimental over a dog and the veterinarian who talks her into adopting it. Kim makes a properly belligerent smart-assed “brat with a death wish” foil, someone who has absorbed the “you’re killing a bug” ethos of their line of work.

But the cluttered backstory meant to flesh out the present day relationship dilemma just serves up more mayhem — one woman or punk with a knife slashing through mobs of minions and the like. The ingredients of an over-familiar formula are right there, letting us know more or less exactly where all this is going, lowering the stakes along the way.

There’s a grace note, here and there. One victim from their profession talks of how one knows the end is nigh — ghosts appear while they’re doing the work.

“Those who miss you come to greet you” upon death. Even hitmen and hitwomen, apparently.

Still, the film never quite transcends the “mixed bag” treatment of a weary genre that it is. We know who she is and how she got this way, but the lack of interior life leaves the character cold as a corpse, with little chance for the viewer to warm up to her.

Rating: unrated, bloody violence

Cast: Lee Hye-yoeng, Kim Sung-cheol, Kim Mu-yeol and Yeon Woo-jin

Credits: Directed by Min Kyo-dong, scripted by Kim Dong-wan and Min Kyo-dong, based on the books by Gu Byeong-mo. A Well Go USA release.

Running time: 2:05