A distinct element of sadness and disappointment runs through Christopher Guest's mockumentaries Waiting For Guffman, Best In Show, and the new A Mighty Wind. Guest's misfits and eccentrics are blindly willing to follow their dreams no matter where they lead, even if they have to practice their craft in the shadow of a roaring roller coaster, or amid the din of a trade show. A Mighty Wind turns that undercurrent of heartbreak into a raging tsunami, thanks to the touching performances of SCTV veterans Eugene Levy and Catherine O'Hara, playing a honey-voiced folk duo whose troubled relationship stands in sharp contrast to the dewy romanticism of their music. A Mighty Wind derives its biggest, most sustained laughs from the beyond-suicidal despair expressed in the covers of Levy's despondent solo albums, but for the most part, the film allows Levy and O'Hara's relationship to remain almost unbearably sad. That sometimes hurts the film's comic momentum, but yields huge dividends during its knockout, emotionally satisfying climax. Hewing closely to the formula of Guest's previous films, Wind centers on a memorial concert that brings together three famed folk acts, including The Folksmen, played by the reunited Spinal Tap trio of Guest, Harry Shearer, and Michael McKean. As the concert date nears, old friendships and feuds are rekindled as the musicians deal with a past that can't help but overshadow the present. Nearly all of Guest's repertory company returns, including Bob Balaban, Parker Posey, Ed Begley Jr., John Michael Higgins, and Best In Show standout Fred Willard, who finds another wonderful conduit for his brand of cheerful idiocy in the form of a comedian who draws from a never-ending font of hackneyed catchphrases and bad ideas. But the film's heart and soul belong to O'Hara and to Levy, whose folk-music burnout has the shell-shocked expression of someone who's been to hell and never quite made it back. A Mighty Wind predictably provides some of the biggest laughs of the past year, but the fragility of O'Hara and Levy's relationship constantly tugs it toward the tragic side of the tragi-comic equation.