In “Snitch,” Dwayne Johnson delivers a strong, disciplined performance as an ordinary civilian trapped in a Kafkaesque corner of the legal system. He plays John Matthews, owner of a successful construction company. The solid businessman finds his life’s blueprint crumbling when his 18-year-old son Jason (Rafi Gavron) gets a mandatory minimum 10-year prison sentence for playing a minor role in a friend’s drug-distribution scheme. No plea bargains, no compromise, no clemency, no exceptions.

Desperate to save his frightened son from predatory cellmates, Matthews makes a deal with icy U.S. Attorney Joanne Keeghan (Susan Sarandon), the only official with the power to reduce Jason’s sentence. Matthews will go undercover to obtain evidence against local drug supplier Malik (Michael Kenneth Williams), giving the politically ambitious prosecutor a boost in her run for Congress. Soon he’s in hopelessly over his head, a pawn in the federal war with Mexico’s lethal narco cartels.

“Snitch” is being marketed as a guns-blazing, bone-crunching exploitation movie, but it’s something more. The surprise of the film is that while it boasts tense, jittery camerawork and builds to a bombastic climax, it’s a serious drama about how a pragmatic man might handle himself in life-or-death circumstances.

His self-sacrificing plunge into danger for his son is fueled partly by a sense of guilt. Jason and his mother live modestly while Matthews, his new wife and young daughter occupy a McMansion. The sprawling home, seemingly so solid, mocks the precarious foundation of Matthews’ comfortable life. One wrong move starts the dominoes tumbling and soon both his families’ lives are endangered.

The screenplay by director Ric Roman Waugh and Justin (“Revolutionary Road”) Haythe devotes generous attention to even its secondary characters and the social fallout of the war on drugs. They set up parallel family stories involving an ex-con employee (Jon Bernthal) who Matthews pressures for introductions to the drug world, and even with the cartel’s lethal point man (Benjamin Bratt).

Waugh, a onetime stuntman, stages the electrifying climactic chase and shootout without any computer-generated folderol. He gives you a hulking semi, four fast cars, a bunch of guns and a scrapyard’s worth of wrecked sheet metal. But he also gives you terror, disorientation and pain when bullets meet bone, rather than phony thrill-ride heroics.

Johnson sets aside his action-man machismo to play an average Joe. His stone-cold terror at being enmeshed with animalistic criminals is utterly convincing. When soft-spoken psychopath Malik thrusts a pistol in his face and taunts, “Never had no iron in your grill before, have you?” Johnson flinches just as any middle-aged desk jockey would. Johnson’s bulked-up, skinheaded hard-case appearance often blinds us to what a versatile and compelling actor he can be. “Snitch” is a welcome reminder.