Where the truth lies is, apparently, somewhere in the vicinity of Kevin Bacon’s rear end. Thereabouts you’ll discover the secret to Atom Egoyan’s silly new sex thriller, a feckless retread of “Mulholland Drive” that devolves into the trashiest gay panic extravaganza this side of “Basic Instinct.” Would that Paul Verhoeven had juiced up this art-house raspberry: Never mind the truth, where’s the sense of humor?

Alison Lohman stars, most dimly, as Karen O’Connor, a bubblegum journalist trying to scoop the scandal that ruined the showbiz partnership of Lanny Morris (Mr. Bacon) and Vince Collins (Colin Firth). Prone to nasty fits of rage, groupie exploitation, and psychosexual repression, this Lewis and Martin-style duo called it quits, understandably enough, when a girl was found dead in their New Jersey hotel bathtub.

“Where the Truth Lies” jumps back and forth from O’Connor’s investigation in early 1970s Los Angeles to the events of two decades past, relishing every design cliche in the book; the ersatz aesthetic is less Noguchi than Ikea. Would-be weirdness abounds: psychedelic “Alice in Wonderland” routines; Lynchian lesbian trysts; a crateful of lobsters on ice, to be served with a saucy side of the bizarre.

Messrs. Bacon and Firth acquit themselves with admirable, if pinched, conviction, but poor Ms. Lohman is a casting disaster. A less credible journalist may never have been put on film. One almost suspects she’s entered a secret pact with her director to fashion some kind of derisive meta-ditz, but to what end? Her fatuous facade never cracks; the truth of the movie is unadulterated foolishness.

Mr. Egoyan angles for a greased-up slide down the rabbit hole of pop postmodernism, but the result is all clog, a mess of faux-scuzz and pretensions. Dramatically preposterous and intellectually trite, “Where the Truth Lies” is merely boring as an art-house T&A flick. The simpletons at the MPAA were sufficiently scandalized by an uptight menage-a-trois to bestow the dreaded NC-17 rating, proving yet again that censors need to get out more often.

“Where the Truth Lies” premiered at the Cannes Film Festival alongside David Cronenberg’s “A History of Violence,” another brainy Canadian mediation on life and lies in America. Facing off in competition, the dueling compatriots came armed with movie stars, genre tropes, and relatively big budgets; both were anticipated as mainstream moves by astringent auteurs. Mr. Egoyan’s muddled riff on noir gave the festival its first juicy fiasco, Mr. Cronenberg’s lucid use resulted in a masterwork.

Where the difference lies is in persistence of vision and integrity of intent. For Mr. Cronenberg, selling out is the new keeping it real: “A History of Violence” behaves like a shopping mall movie in order to critique shopping mall culture. “Where the Truth Lies” looks like “Showgirls” sans vulgar verve, crossed with “L.A. Confidential” playing itself. It’s a mega meta bore.