One of the oldest and most enduring conspiracy theories is that the plays attributed to William Shakespeare were not actually written by him. The controversy first arose some 250 years after Shakespeare’s death, and it basically boils down to the notion that no one as uneducated and lowly in station as he could have written such masterful works. Like most conspiracy theories, it is favored by people who are less smart than they think they are, and can only be believed by ignoring the known facts in favor of convoluted speculation.

Still, it can make for an entertaining story. What if Shakespeare’s plays were written by someone else?? I mean, they weren’t, make no mistake there. But what if they were?? That is the basis of “Anonymous,” a dumb but amusingly told faux-historical drama by director Roland Emmerich, who’s best known for disaster movies like “Independence Day” and “2012.” It’s tempting to say “Anonymous” is a disaster of its own kind, but that’s not quite true. The costumes, production design, and cinematography are splendid, and the acting is respectable. The only problem is that it’s all in the service of such a goofy premise, further complicated by an Elizabethan soap opera story line that topples into ridiculousness.

We open on a modern theater stage, with an actor (Derek Jacobi) delivering the prologue much the same way that an actor in one of Shakespeare’s (or whoever’s) plays would. He informs us that we are about to see the story of the Bard, but that it’s not the one we’ve heard before. “Let me tell you a different story,” he says melodramatically. “A darker story — of quills and swords!” OK then!

From there we are transported to London circa 1600. Edward de Vere, the Earl of Oxford (played by Rhys Ifans), has a compulsion to write plays, yet cannot do so publicly because his puritanical father-in-law, William Cecil (David Thewlis), believes such artistic expression to be devilish. The two are at odds on political matters as well. Cecil, an adviser to Queen Elizabeth (Vanessa Redgrave), favors the choice of James of Scotland to be her successor; Edward is of the faction that favors the Earl of Essex (Sam Reid). The question is important, as Elizabeth has no natural heirs (OR DOES SHE??).

After seeing a play at the Globe Theatre that lightly satirizes Cecil, and observing how expertly it manipulates the crowd’s opinion, Edward decides he can wait no longer. He buttonholes playwright Ben Jonson (Sebastian Armesto), gives him a script he’s written, and persuades him to claim it as his own. Yet in a farcical series of events, credit for the play, “Henry V,” is taken by William Shakespeare (Rafe Spall), a crass, raucous actor who can read well enough to learn his lines but can’t write a word. He certainly couldn’t have written — couldn’t have even conceived — something as complex as “Henry V”! But he claimed credit publicly, so whaddaya gonna do? Edward is stuck with Shakespeare as his sock puppet, delivering plays to him that are designed to whip the public into a patriotic, pro-Essex fervor.

Mixed with all of this political intrigue and theatrical skulduggery are flashbacks to an earlier time, when a young Edward (Jamie Campbell Bower) had an affair with a young Elizabeth (Joely Richardson, who looks the part because she’s Vanessa Redgrave’s daughter). We learn the sordid details behind Edward’s arranged marriage to William Cecil’s daughter, Anne (Helen Baxendale), who doesn’t approve of his playwriting any more than her father does. Through it all, Edward writes anyway, hiding his plays and poems so that he has quite a stockpile by the time he hooks up with Shakespeare.

All of this would be fine if it were presented for what it is: an implausible, slightly campy alternate version of history. The screenplay, written by John Orloff (OR WAS IT??), who also wrote “A Mighty Heart” (OR DID HE??), throws a few bones to Shakespeare fans by showing incidents in Edward’s life that would later turn up in his plays: an eavesdropper being stabbed while hiding behind an arras, for example, as was Polonius. Orloff also comes up with some ludicrous plot twists that, under the right circumstances, would be laughable.

It’s hard to tell how Orloff intended his screenplay to be interpreted, but what sinks “Anonymous” is the pervading sense that Emmerich, the director, wants us to take it seriously. He doesn’t mean it as a lark — he really believes the Edward de Vere theory, and seems to have made the film as an earnest attempt to share the “truth” with people. As the movie goes on and on (and on and on), it starts to feel like a breathless harangue. I enjoy a fairy tale as much as the next person, but not when it’s presented as if it were actual history.

C+ (2 hrs., 10 min.; PG-13, a little sexuality, a little violence.)