The intersection of mystery and epistemology can be a lively place to set a film, as Alain Resnais and his many imitators have demonstrated. The Whodunit? agenda of the standard Agatha Christie–style yarn becomes the much more complex Did someone do something? And, if so, how do we know? That’s a gambit that would naturally appeal to writer-director Atom Egoyan, who prefers that his movies (among them The Sweet Hereafter and Ararat) unpeel like an onion. It also hooked Marc Forster, who after following Monster’s Ball with Finding Neverland is clearly intent on not doing the same thing twice. Alas, both filmmakers’ latest efforts ultimately yield to routine explications. Before they deflate into mere intrigues, however, Egoyan’s Where the Truth Lies and Forster’s Stay scramble reality with agreeable gusto.

An accidental companion piece to Capote—and to Jerry Lewis’ new memoir—Where the Truth Lies is another inquiry into celebrity and corruption in pre-HBO America. Watergate is about to sully the country’s innocence when young reporter Karen O’Connor (Alison Lohman) begins to probe the untold story of former song-and-joke partners Lanny Morris (Kevin Bacon) and Vince Collins (Colin Firth), whose similarity to Jerry Lewis and Dean Martin is no fluke. But the suppressed scandal at the heart of their story happened back when Eisenhower was president and Lanny and Vince were conducting telethons to battle polio. In those days, the after-show party could get wild, but what happened backstage stayed backstage. So it’s never been revealed just how that beautiful blond corpse appeared in Lanny and Vince’s suite in a mob-controlled New Jersey hotel, shortly before the two men ended their partnership.

Adapted from a novel by Rupert Holmes—yes, the piña-colada guy—Where the Truth Lies could have been an ordinary murder mystery punctuated by a few yearning sighs for lost showbiz glamour. Yet Holmes’ scenario includes elements that mirror Egoyan’s long-standing concerns, notably baroque sex (Exotica) and surveillance (Family Viewing). Lanny and Vince take drugs and whichever women they want, including Karen and the victim, Maureen O’Flaherty (Rachel Blanchard), another aspiring reporter. Maureen’s death occurs in the ’50s, so there’s no video, but there is an audio recording with incriminating details. And 15 years later, during one of the movie’s fateful threesomes, photographs are taken. As so often in Egoyan films, titillation and blackmail are just two possible readings of the same image. (The sex is not explicit, but the kinky ambience was enough to draw an NC-17, which the distributor ducked by releasing the movie unrated.)

Gliding between 1957 and 1972 on cinematographer Paul Sarossy’s fluid camera movements, the director stuffs the film with subtext, associations, and asides. If Lanny and Vince are duality in action—a “boy-girl act,” as the former puts it—Karen is two women in one (or six in three). In addition to being the dead Maureen’s symbolic doppelgänger, Karen also appears in the film as a ’50s girl and ’70s woman, and briefly becomes Lanny’s lover while posing as her best friend, Bonnie. Egoyan conflates Lewis Carroll and David Lynch, arranging an L.A. orgy to the strains of “White Rabbit,” and stages the mystery’s breakthrough conversation on the streets of a Hollywood back lot, so as to assert the moment’s artificiality. The roles of clowning philanthropists, played in public by the secretly ruthless and self-serving Lanny and Vince, are hardly the only hollow edifices on display.

Compellingly balmy as some of this stuff is, Egoyan eventually accepts Holmes’ plot, which involves numerous affronts to history and common sense. The murder’s solution turns on fear of an exposé that never would have happened in the ’50s, when stars’ illicit idiosyncrasies were routinely concealed by the entertainment press. The story also involves frequent handling of the corpse—the effects of which would have caught the attention of any coroner, even one using ’50s technology—as well as a killer whose identity Ms. Christie herself might have rejected as hopelessly hackneyed.

Perhaps the picture would have been convincing with actors who played both sides of their characters with equal confidence, but Bacon and Firth are much more believable as offstage louts than as onstage charmers, and Lohman’s bland performance consists principally of wide-eyed looks and plunging necklines. Where the Truth Lies is a relatively big-budget, relatively mainstream project for the Canadian art-film director, and someone or something induced him to cast bankable stars—such Egoyan stock players as Don McKellar and Arsinée Khanjian have only cameos—and offer a tidy resolution. It’s the movie’s messy parts, however, that fitfully fulfill the promise of Holmes’ jokey title. CP