It takes forever to get going, and lollygags along even after that.

As a businessman scrambling to find a way to get his son’s Federal prison sentence cut, Dwayne “The Rock” Johnson has to play fear, tough love, pity and panic – and he’s a bit in over his head.

But that’s the point of “Snitch,” a straight-no chaser thriller “inspired by a true story.” The pacing is off, too many scenes lack dramatic punch and play like filler. But Johnson is pretty good at being a guy in over his head, sharing scenes with flinty pros like Susan Sarandon, Benjamin Bratt and Barry Pepper.

It’s a tale of a Middle American civilian who gets mixed up in the Feds vs. Mexican drug cartels war, one whose “mandatory minimum sentencing” has snared John Matthews’ naïve 18 year-old son. The prosecutor (Sarandon) is a hardcase, readying a run for Congress. So John makes a deal – I’ll get “an introduction” into that world through my construction supply business. I’ll use my Jefferson City, Mo., trucks for transport, and you’ll nail Big Players from the cartel.

Co-writer director Ric Roman Waugh is a stuntman turned director. But he wastes a staggering amount of time setting that scenario up, and even more time getting to the point where his straight-no digital stunt experience pays off. Some of that establishes that John is a fish out of water and shows us his learning curve. Mostly, though, that slow pacing robs the story of tension and suspense.

What gives it’s juice is the supporting cast. John Bernthal (“The Walking Dead”) is credibly wary as the ex-con John begs to get him in the door of the drug world. And the terrific Michael Kenneth Williams is the first dealer he meets, a guy who pulls a gun on him just to test him.

“Ain’t never had no iron in your grill before, have you?”

Waugh can be forgiven for giving these guys more scenes than are absolutely necessary. They’re that good.

Pepper (“Broken City”) sports a Civil War worthy goatee in his role as an undercover Fed who frets over John’s safety. Ravi Gavron is properly frightened as the boy who let a friend entrap him with a box full of pills and sets this whole saga in motion, though Waugh loses track of the kid for much of the movie. We need reminding of the stakes, the danger.

But I like the way Johnson, often shot in extreme close-ups, underplays this guy. And I like the way the script lets John’s ineptitude and discomfort in this world create the humor, the way Waugh has some scenes set to music, no sound effects, the way he dispenses with the obligatory “I’m gonna need to head to the gun shop” scene and the way the man films a car and truck chase – rending metal, shattered glass, none of this digital fuss and fakery.

“Snitch” isn’t a great film. But after the run of brawling, over-the-top shoot-em-ups/drive-em-ups that have cluttered Johnson’s resume it’s good to see him try his hand at acting, even if he is just as over-matched as the fellow he’s playing.

MPAA Rating: PG-13 for drug content and sequences of violence

Cast: Dwayne Johnson, Susan Sarandon, Barry Pepper, Benjamin Bratt

Credits: Directed by Ric Roman Waugh, written by Justin Haythe and Ric Roman Waugh.  A Summit release.

Running time: 1:52