In the Coen brothers' Barton Fink, budding screenwriter John Turturro is stuck on his first assignment, a Wallace Beery wrestling movie. Studio executive Tony Shalhoub, recognizing the finite possibilities presented by the shopworn combination of star and story elements, offers terse advice: "Wallace Beery. Wrestling picture. What do you need, a road map?" Somewhere, the spiritual descendants of Shalhoub's character have probably offered similar counsel to writers assigned to work on Martin Lawrence vehicles. Lawrence's latest, which transports the wisecracking star to the Middle Ages, plays less like a movie than the inevitable result of colliding elements: one part Lawrence, one part A Connecticut Yankee In King Arthur's Court, and a whole lot of fish-out-of-water comedies from years past. Of course, that assumes that writing factored in at all. Few comedians since Jerry Lewis have seemed as uncomfortable with silence as Lawrence, whose ad-libs fill out every scene. Most of the time, they hardly count as jokes. After falling in a magic body of water at Medieval World, the rundown theme park where he works (and, as one character boasts, a source of "quality jobs for 27 years"), Lawrence emerges in Ye Olden Times with the comment, "Oh shit! The water's cold." Even if his delivery made that resemble comedy, nothing else would. So it goes throughout Black Knight, as Lawrence uncovers an evil scheme to keep the rightful queen from the throne and teams up with a disgraced knight to set the matter aright. Along the way, he pauses to romance a pretty chambermaid, and to teach a crowd of feastgoers to get jiggy to a lute-and-bugle version of Sly & The Family Stone's "Dance To The Music." "You speak with an unusual tongue," comments one character, perhaps referring to Lawrence's ability to squeeze extra vowels and syllables into the word "damn," or to punctuate virtually every scene with the exclamation, "Oh shit!" By now, his shtick feels almost medieval itself, but Lawrence, who executive-produced Black Knight, might have at least sprung for a better home for the material. Shot in the ancient kingdom of North Carolina, the film limits its action almost entirely to the woods and a set nearly as cheap-looking as Medieval World itself. Maybe the production designers lost their road maps.