Although it sometimes accompanies fine films such as Zero Dark Thirty and Argo, the phrase “inspired by a true story” tacked onto the front of a movie too often warns you that you're about to see something “inspiring” in the most hackneyed, triumph-of-the-human-spirit sort of way. What's surprising about Snitch is that, rather than taking the reductive path of offering innocuous emotional uplift or one-man-army action, it generates a feeling of real desperation and fear as it shows a man getting in way over his head when he takes on some very bad guys. In other words, this is a pretty good film starring an actor named Dwayne Johnson, not a commodity with The Rock as a hood ornament. Summit's main commercial hopes still rest with the mainstream action crowd -- which likely will be satisfied despite the film's refusal to dish out doses of bodily harm like clockwork -- but for Johnson, this could broaden the perception of the sorts of roles he can play as he pushes into his 40s.

Directed with intensity by longtime stuntman Ric Roman Waugh (Felon), Snitch takes its dramatic opportunities seriously and not just as an excuse for brutal confrontations between drug dealers and assorted thugs. The “inspiring” part lies in the fact that a father, John Matthews (Johnson), is willing to go to the absolute limit to prevent his teenage son Jason (Rafi Gavron) from serving 10 years in prison under mandatory-sentencing laws for having made one stupid mistake. The involving part is how he goes about it: getting entangled with some very unsavory characters while trying to preserve a vestige of his morality and remain alive.

Inspired by a Frontline report about an aspect of the law that allows for reduced time in exchange for informing on drug dealers, the script by Justin Haythe (Revolutionary Road, The Clearing) and Waugh follows a familiar-feeling template but goes deep enough with character detail and legal issues to set it apart from standard-issue drug- and crime-related films. Jason gets sent away for ill-advisedly accepting delivery of a box full of Ecstasy as a sort-of favor for a friend and also in order to try it with his girlfriend.

Unwilling to rat his buddy out, the terrified, physically unprepossessing Jason is tossed into the pen, where he'll be as defenseless as a rabbit in a foxhole. His resentful mother (Melina Kanakaredes) lashes out at John, her ex, while the only solution offered by politically hungry U.S. Attorney Joanne Keeghan (Susan Sarandon) is for Jason to offer evidence against some other drug dealer, but he truly doesn't have any.

The biggest dramatic leap the film imposes is that John, a straight-arrow guy who runs a shipping company but suffers guilt over having been a deficient dad post-divorce, would conceive of and then persuade the attorney to accept a plan under which he himself would deliver drug dealers to her in exchange for his son's freedom. Keeghan expresses the same dubiousness the audience might feel, but once John gets the green light, you can feel the sweat and inner turmoil begin to simmer, as he's no better-suited than Homer Simpson to figure out how to go about this. John's formidable physique and straight-shooter personality might serve him well in most situations, but they have little bearing given his new challenges.

Reluctantly, John leans on one of his employees who has done time, Daniel Cruz (Jon Bernthal), to point him in the right direction -- a wrenching decision in that the man, who has a son of his own, is trying to stay straight. But John finally gets entree to dealer Malik (a terrific Michael Kenneth Williams), a two-time loser who, after some tense testing, agrees to use him on an out-of-state drug run.

The first big action scene doesn't arrive until an hour in, at which point the stakes grow much higher with the involvement of a U.S. branch of a Mexican drug cartel run by the cool Juan Carlos (Benjamin Bratt). With her congressional race heating up, the idea of bringing down such a big dog excitesKeeghan to no end but puts John and Daniel in untenable positions, leading to some tough choices for both men. The danger they face feels real, as does their angst over moral compromises, and the film climaxes in a well-staged chase involving John's 18-wheel big rig that presumably draws upon the director's stunt experience in achieving such old-school, real-deal power.

Unusual for this sort of thing, Snitch is a film after which you remember the characters and actors more than the big action moments. Never removing his shirt, Johnson behaves within a narrow range but is engagingly distressed and stalwart in equal measure, conveying sufficient feeling and subtext to suggest the actor could be entrusted with greater dramatic challenges in the future. Bernthal (The Walking Dead) strongly puts over a conflicted man pushed into a terribly precarious position, andBarry Pepper keeps you guessing as a hipster-looking undercover cop. Sarandon's ambitious crime-buster remains unfortunately one-dimensional.

Waugh and sharp-eyed cinematographer Dana Gonzales keep their framing quite tight, which amplifies the actors' work but, more ambiguously, keeps you worried about what might be going on outside the field of view. A very large contribution is made by Brazilian composer Antonio Pinto(City of God, Senna, Get the Gringo), whose eerie, ever-hovering electronic score gathers cumulative force to greatly amplify the story's power.