When does a highly watchable movie stop being a beacon of enjoyment and turn into a morally reprehensible insult? For one, when its name happens to be "Law Abiding Citizen," an absorbing-turned-ludicrous thriller that gets more exploitative, ugly and dishonest the longer it plays out. Director F. Gary Gray (2005's "Be Cool") and scripter Kurt Wimmer (2008's "Street Kings") show precious little restraint as they tackle a project that tries to cross "The Silence of the Lambs" with "The Shawshank Redemption" while going so far over the deep end that it ends up making a mockery of itself.

After his wife and daughter are brutally murdered by a pair of thugs who break into their home, grieving widow Clyde Shelton (Gerard Butler) is outraged when prosecuting attorney Nick Rice (Jamie Foxx) arranges for one of them to testify against the other in exchange for a shortened, tidy three-year prison sentence. Ten years later, Rupert Ames' (Josh Stewart) scheduled execution by lethal injection goes awry after his drug doses are mysteriously tampered with, and long-released partner-in-crime Clarence Darby (Christian Stolte) is kidnapped by Clyde and subsequently tortured and maimed. Clyde is promptly arrested despite his claim that there is no concrete evidence to convict him, and then begins toying with Nick and his surrounding authorities. As Clyde, a tinkerer and inventor of gadgets, begins masterminding a series of murders even as he is stuck behind bars, an increasingly racked-with-guilt Nick has little choice but to play by his rules as the city of Philadelphia drops to its knees in fear of what might be waiting around the corner.

Once the artificially dramatized prologue is over, complete with slow-motion stylizations and echoing screams of protest as Clyde watches his family killed in cold blood, "Law Abiding Citizen" improves considerably. The film's first half might be a little trashy, but it is also taut and riveting, with Clyde seeking vengeance for the loss of his beloved spouse and child while rightfully putting to task a flawed judicial system that sets guilty people free and occasionally leaves innocent people wrongfully accused. He might not have made all the right choices, but Clyde's actions up to this point are understandable considering the tragedies that have befell him. That flies out the window soon after as Clyde becomes a methodical serial killer, taking lives of innocent people who only have inconsequential ties to the initial case involving Ames and Darby. As Nick investigates how he is pulling off his dastardly deeds while stuck in solitary confinement, a remorseless Clyde becomes no better than the monsters that stole his family from him.

Where the picture travels from here is on a consistent downward decline as suspension of disbelief is demanded in order to forget how many plot holes are being left in its daffy wake. The revelation of how Clyde has been carrying out a killing spree from within a jail cell is loonier than one could possibly imagine. Nick makes for an unsympathetic, decidedly smarmy protagonist as he clings to his highfalutin belief that he is the best at what he does despite his past decisions being one of the central causes for the present-day crime wave. Nick does recognize the sanctimoniousness of what Clyde is doing and tries to get through to him how many innocent families he is destroying because of his own hell-bent rage—"how would your wife and daughter feel about what you're doing?" Nick asks him at one point—but the film turns right back around in the third act and becomes doubly hypocritical. What Nick rashly does at the end is distasteful, repugnant and enraging, leaving the viewer feeling unclean as our would-be hero skips off to his ten-year-old daughter's school recital without caring about or taking responsibility for his own indefensible actions.

Gerard Butler (2009's "Gamer") is cool, calm and maniacal as the brilliant, if loose-screwed, Clyde, and Jamie Foxx (2009's "The Soloist") is controlled and relatively believable as attorney Nick. In several cases, however, Foxx is upstaged by his supporting co-stars. Leslie Bibb (2009's "Trick 'r Treat") brings a warm reliability and tinge of regret to her role as assistant Sarah Powell, who has watched her years of dedication to Nick slip by. Annie Corley (2006's "Stick It") deliciously chews up the scenery as the power-happy Judge Laura Burch, exiting the proceedings with a memorable stunner of a scene. Viola Davis (2008's "Doubt") exudes power and an underlying sense of unease as the Philadelphia mayor, a woman none too appreciative of her loss of control over her city. In a too-rare serious turn, Regina Hall (2006's "Scary Movie 4") plays Nick's wife Kelly, a relatively thankless role, but one that she dutifully fulfills with gusto.

"Law Abiding Citizen" is a motion picture of two distinct sides, meshed together uncomfortably. On the one hand, it does garner the viewer's rapt attention and includes enough twists to keep a person engaged and guessing where things are headed. On the other hand, where things do lead would be laughable if they weren't so fundamentally unconscionable. As the story of a man who loses his lifeblood and wants payback, "Law Abiding Citizen" jumps the rails and ends up not knowing what it wants to say. There are no lessons for Clyde or Nick to learn because they are too busy doing awful things. That the film seemingly condones Nick's criminal decisions in the final stretch is more disturbing than any of its copious violence and bloodshed.