Medieval murder mysteries are rare enough on the big screen–“The Name of the Rose” dates back to 1986, after all–that even an imperfect example is a noteworthy event. So while as a narrative this new example, “The Reckoning,” is seriously flawed, with a final revelation that’s far too obvious, it does conjure up a menacing, foreign environment that’s sporadically compelling. Still, a mystery that’s mysterious only in mood and not in plot is unlikely to satisfy most viewers.

Adapted by Mark Mills from Barry Unsworth’s novel “Morality Play,” the story centers on a group of players, headed by Martin (Willem Dafoe), traveling to a distant castle to perform for a nobleman in the England of 1380. They’re joined by Nicholas (Paul Bettany), a fugitive priest on the run after he was caught in a distinctly compromising situation with a local woman by her furious husband. (The villagers are vigorously pursuing him.) A demolished bridge forces the group to detour into a town where they encounter the conclusion of a trial in which Martha (Elvira Minguez), a mute, is found guilty of murdering a boy. When the troupe’s performance of one of their standard biblical plays–the fall of Adam and Eve–fails to bring in enough revenue to cover their expenses, revolutionary-minded Martin suggests that they stage a new piece dramatizing the recent killing. He and Paul investigate the case to write a script, in the process discovering not only that other children have been murdered too, but also that Martha was religiously suspect because she claimed to be a healer. It’s further revealed that Damian (Ewen Bremner), a sinister monk, was instrumental in the accusation leveled against her, and that he in turn is connected with the local lord (Vincent Cassel), about whom many dark rumors circulate. There’s also a royal justice lurking about, interested not only in the murder but also in wider political issues. The denouement finds the real culprit and his motive revealed and Nicholas finding redemption for his sins.

This plot cannily touches on a good many of the major issues of late fourteenth-century English history, though it doesn’t spell them all out very clearly. The most obvious, perhaps, is the artistic one involving the changing nature of drama, which was in fact moving away from the traditional mystery plays based strictly on Scripture to more imaginative human morality tales. The periodic recurrence of the bubonic plague, which had first struck some three decades earlier, is also alluded to, as is the difficult political and social situation, though more obliquely. (Young King Richard II had only recently ascended the throne, his uncle John of Gaunt was still angling for real control, and the economic complaints of the lower classes were festering–1381, after all, witnessed the so-called Peasants’ Rebellion.) But “The Reckoning” doesn’t build a thoroughly satisfying drama against this fascinating backdrop. The crux of the mystery becomes apparent too soon, so that what’s intended as a surprising revelation lacks punch, and while the way the villain is ultimately dealt with has a certain plausibility within the context of the time, its emphases seem more modern that medieval. Paul McGuigan directs too languidly, toning down the frantic style he used in “Gangster No. 1” overmuch. And the characters simply aren’t drawn, or acted, sharply enough to make up for the deficiencies in plotting and pacing. Nicholas is meant to be a troubled, fatalistic fellow, but Bettany plays him at too high a pitch. Martin, on the other hand, remains overly enigmatic; he clearly feels a drive to modernize his plays, but where that impetus comes from is never clarified, and though Dafoe exhibits a remarkable physical dexterity in the role (a sequence of him limbering up before a performance borders on the amazing), his performance shows more brusqueness than subtlety. The supporting players, good as they are, are let down by characterizations that seem little more that sketches. Cassel exudes oily arrogance as Lord De Guise, but it’s a one-note turn, as is Bremner’s as Simon, the monk, while Gina McKee is astonishingly underused as Martin’s sister Sarah. Even the redoubtable Brian Cox is notable for little else but his burly frame and bulldog visage as the troupe’s resident grumbler, Tobias.

In fact, where “The Reckoning” excels is in its recreation of the medieval milieu, which is on a par with that of “The Return of Martin Guerre.” Production designer Andrew McAlpine constructed a marvelously authentic village set, complete with a castle towering over the peasant houses, in Spain, and it’s well captured by cinematographer Peter Sova: the bleakness and cold are almost palpable. The portrayal of the troupe’s dramaturgical apparatus is excellent, too.

Ultimately, however, it’s difficult to embrace a film that’s notable more for its outward appearance than its content. In the final reckoning, this modern version of a medieval morality play, with its fine surface but problematic plot, proves more impressive for its body than its soul.