In the Middle Ages, a dreadful crime has been committed and only the burning, defiant beacon of dramatic theater can illuminate the true culprits.

Tantalizing premise, inept execution. “The Reckoning” — based on Barry Unsworth’s historical novel set in the 14th century, “Morality Play” — flickers only briefly before collapsing into a yawning darkness of rotten scripting and woefully affected direction. The only thing this wayward mystery truly illuminates is star Willem Dafoe’s fondness for yoga.

Director Paul McGuigan has a fundamental problem: His characters neither look nor sound like 14th-century Brits. This is even true of Paul Bettany, so flamboyantly good as Geoffrey Chaucer in “A Knight’s Tale,” but somewhat less compelling here as Nicholas, a disgraced priest hoofing it through the countryside, fleeing his sin-ridden past. From the outset, Bettany seems ill-suited for the role; too boyish, too cultivated, too hidebound determined to project leading-man intensity.

Just as off-key is Dafoe, playing the leader of a troupe of itinerant actors who stumble upon Nicholas in the forest and quickly adopt him into their fold. For whatever reason, the immensely talented Wisconsin native proves utterly incapable of a consistent accent. Sometimes he sounds British, sometimes Dutch, sometimes like the guy who sells you bratwurst at Brewers games.

By and by, Nicholas and his dirt-poor thespian friends visit a prosperous township ruled by a Norman lord (French actor Vincent Cassel) where the murder of a teenage boy has scandalized the locals. Discouraged by the low turnout for their usual Bible-inspired parables, Dafoe’s character, Martin, comes up with a truly visionary plan: Why not dramatize the boy’s murder as a lesson in morality and consequence?

Needless to say, the play is a hit. It also exposes the murder trial as a sham, emboldening the townsfolk to speak up about other missing and murdered children. Nicholas, determined to redeem himself, quickly grows a backbone and vows to expose the real evil lurking in the castle above. McGuigan — who also helmed an adaptation of Irvine Welsh stories called “The Acid House” (1998) — has the filmmaking sensibilities of an 18 year old MTV intern.

An important movie is trapped somewhere in “The Reckoning” — one buried alive by filmmakers who lack the sophistication and subtlety to reconcile an exotic, faraway premise with modern- day themes. Ultimately, “The Reckoning” is less about the revolutionary power of theater — much like Tim Robbins’ vastly underrated “Cradle Will Rock”— than an object lesson in the perils of artistic self importance.