There is a grittiness in Joe Carnahan’s “Narc” that seems forced. In the film’s opening moments, a man is stabbed in the neck, causing him to choke on his own blood; and then a pregnant woman is shot. All of this is accompanied by realistic screaming and commotion that may give the film “street cred,” but which also smells like a case of trying too hard.

For when you boil it down, “Narc” is just like a thousand cop dramas before it, and in particular like a lot of TV shows that focus on loose-cannon law-enforcement officers. The crazy one here is Henry Oak (Ray Liotta), a brutal narcotics officer whose partner was recently killed. Pretty much the only significant difference between Oak and the protagonists in “NYPD Blue” and “The Shield” is that they can’t say the F word; you can see, then, why the film would try so hard to convince us it’s not just another cop drama.

Oak is joined in his search for his partner’s killers by Nick Tellis (Jason Patric), a former narc who has been taken out of active duty after making some questionable decisions in a moment of crisis. His wife, Audrey (Krista Bridges), wants him safe, and he wants the same thing: In exchange for a cushy desk job, he agrees to help find the cop killers.

The path is not smooth, of course, and Tellis learns things about the dead cop that Oak either didn’t know or chose to ignore. It affects Tellis’ marriage, which is nothing more than obligatory; curiously brought up and then disregarded is the idea that the police force is looking for a scapegoat in the murder to avoid a race riot.

But it is all very slickly told, and well acted to boot. Jason Patric’s mix of weariness and fervor is perfect for Tellis, and Ray Liotta strikes just the right combination of toughness and believability for Oak. Two possible revelations about Oak’s character are presented, and Liotta has done such a thorough job in establishing the character that, rather than one option being obvious and the other absurd, we find we could honestly believe either of them. (Credit should be given to Carnahan, too, who knows how to include important scenes without labeling them “Important Scene.”)

The plot has one neat little twist, and then another one, and then possibly a third, depending on how you look at it — all just enough to convince us we’re seeing something new. It’s nothing more than an extra-gritty cop show, but it’s a competent one.

B (1 hr., 42 min.; R, pervasive harsh profanity, abundant graphic violence, some brief nudity, a lot of drug use.)