"I've a naughty little tale to tell," the Marquis de Sade informs us as Quills opens. It's actually the opening line to the latest bit of juicy pornography he's writing, but of course it applies to the story Quills tells, a fictional account of de Sade's final years spent in a French insane asylum. As promised, Quills is bawdy and often surprisingly funny, but more frequently it's like a dark and disturbing flip side of Shakespeare in Love, exploring the inner and outer demons that torment and inspire writers and the necessity of leaving writers to exorcise those demons on their own, no matter whose sacred cows get slaughtered.

De Sade (Geoffrey Rush: Mystery Men) lives in relative comfort at the madhouse run by Coulmier (Joaquin Phoenix: Gladiator, 8MM), a Catholic priest; his quarters -- it could hardly be called a cell, except for the fact that the door locks from the outside -- are overrun with books and stocked with fine wines. He continues writing the erotica that landed him there in the first place (his wife had him committed, figuring an asylum would be far preferably to prison), though now his fiction is anonymous and sneaked to the outside world through Madeleine (Kate Winslet: Titanic), a young laundry maid who is a big fan of his work. His Paris publisher can barely keep up with the demand for his latest novel, Justine, but its popularity has caught the attention of Emperor Napoleon, who is infuriated that such "filth" is reaching the streets... and that de Sade has obviously not been cured of his supposed disease. So the emperor sends the alienist Dr. Royer-Collard (Michael Caine: The Cider House Rules, Little Voice) to take over de Sade's case.

De Sade writes made-up tales of torture, perversion, and "the art of pain," but Royer-Collard is an actual practitioner, employing methods he allows are "aggressive" and which his critics decry as "old-fashioned, even barbaric." (Even the portcullis at the gate of his hospital drops with a guillotine-like shudder.) Quills -- directed by Philip Kaufman (The Right Stuff) and based on Doug Wright's play -- makes no bones about which kind of man it considers the sick one. Which is more depraved, Quills demands, the man whose violent tendencies are purely fictional or the one who enjoys actual people actually in pain? Which is more evil: the man who needs to get his wicked fantasies down on paper lest they drive him mad, or the man who takes away the writer's tools, rendering him mute? Which is more perverse: to indulge, at least mentally, in one's every sexual whim, as de Sade does, or to indulge, as the priest Coulmier does, in a masochistic religious passion that disallows all sexual feelings of any kind?

Quills steers you toward its own answer, and it's the standard liberal one: that sin is not defined, to paraphrase George Carlin, by the Invisible Man and his list of ten things he doesn't want you to do, but that the only sin is to hurt someone. The truly naughty thing about Quills is that it dresses its nothing-sacred answer up in as saucy a package as you're likely to find. Never cutesy (as Shakespeare in Love was, if appropriately so), Quills is instead stirring on a lusty, primal level that touches that baser human nature de Sade probed in his work. The film is disquieting when it wants to point out the cruelties that drive the world, from servant girls who rat out their peers to curry favor with powerful men to the terrible reign of Madame Guillotine that colored de Sade's outlook on human nature. Yet it retains a hearty, robust innocence about all that's lewd and wanton. Phoenix and Winslet -- two of the finest young actors on the screen today -- each maintain an ingenuousness that's absolutely right for Coulmier and Madeleine, the young priest and the young maid each seemingly making up for a lack of experience with an unearned sophistication. And Rush's de Sade is the eccentric calm in the middle of a storm of putative normalcy, turning perceived madness into just about the only sanity to be found.

There's nothing in the least bit perverse about Quills. And if there's anything sacred about it, it's that it holds nothing sacred.