“Macbeth” is served up to a McDonald’s recipe in actor Billy Morrissette’s writing-directing debut, which comically transposes the Bard’s tragedy to a fast-food restaurant in a small Pennsylvania town in the early 1970s. There have been funny adaptations of Shakespeare’s Scottish play before–William Reilly’s overwrought Mafia updating “Men of Respect” (1991) comes immediately to mind–but this might be the first one that intends to be so. The humor isn’t biting or vicious–the piece doesn’t go for the jugular in the way that Barbara Garson’s off-Broadway play “Macbird” (which amounted to an accusation that Lyndon and Lady Bird Johnson were behind the assassination of John Kennedy) did in 1966. Rather it has the quality of a loopy, short-lived sitcom or a sophomore sketch in a college revue. Unfortunately, the invention runs out long before the plot does, and in the final third of the picture the laughs are few and far between.

Morrissette’s recycling concerns the fate of Duncan’s, a burger joint where mop-haired Joe McBeth (James LeGros) works as a cook and his wife Pat (Maura Tierney) as a waitress. Following the original plot, Pat prods her laid-back husband to kill the diner’s owner (James Rebhorn) in a staged robbery and then use the proceeds from the heist to purchase the restaurant from Duncan’s slacker son Malcolm (Thomas Guiry); soon the restaurant (renamed McBeth’s) becomes a goldmine as a result of Joe’s improvements (an innovative drive-through window, a traveling fries truck, some special meals). But there are problems: a strange vegetarian detective named McDuff (Christopher Walken) begins investigating Duncan’s death, and three hippies (Andy Dick, Amy Smart and Timothy Speed Levitch), who had already prophesied McBeth’s success, now warn him of the threat posed by his buddy Anthony “Banko” Banconi (Kevin Corrigan), who could undermine his alibi. And, of course, Pat begins going berserk over a burn on her hand, suffered when she and Joe dunked poor Duncan in a pot of boiling grease.

As should be obvious from this precis, “Scotland, Pa.” follows the trajectory of “Macbeth” pretty closely. That isn’t a particular problem early on, when the translation to the America of bell bottoms and shoulder-length hair and the rust-belt east coast is sufficiently peculiar to generate some chuckles, even if most of the cast are so laid-back as to seem relatively listless. The arrival of Walken invigorates things; his customary oddball delivery and hints of self-mockery (as when he offhandedly remarks that he started out as a dancer) bring a needed note of unpredictability to a narrative that grows more and more unimaginative in its reworking of Shakespeare’s plot. By the last act whatever cleverness the conceit originally evinced has dissipated, and the picture goes rather laboriously through the machinations of the play in ways that come across as dutiful rather than inspired. The little amusement that remains arises from mere grace notes, such as the curious activities of Malcolm’s brother Donald (Geoff Dunsworth). By this time Tierney has grown shrill, LeGros’ bumptiousness has become labored, and Corrigan’s lackadaisical cluelessness has degenerated into dullness. Even Walken’s sporadic interventions are increasingly tame.

In sum, Morrissette’s modern riff on “Macbeth” has some bright moments, especially in the first half. But it loses steam down the stretch, and by the time the lights come up, “Scotland, PA” has become one of those movies that one can appreciate more for the idea behind it than for the way in which it’s been executed.

It should be noted that there’s one genuinely amusing aspect of “Scotland, PA,” though it’s something that, unhappily, general audiences won’t even be aware of. That’s the press kit, which has been printed up in the form of an ersatz Cliff’s Notes pamphlet, complete with black-and-yellow cover. This isn’t a new joke–there were the “Spy Notes” on all the angst-ridden novels about young urbans (like McInerney’s “Bright Lights, Big City” and Ellis’ “Less Than Zero”) issued back in 1989, for example, which followed the same style–but, especially to a teacher, it’s still a good one.