It's the 17th century in London town and "the prettiest woman in the whole house" at the Betterton Theater, the one who brings audiences to their feet each time she "dies" as Desdemona, just happens to be, well, a man. The stage custom of the time, this pretense also underscores the nothing-quite-as-it-seems feel of "Stage Beauty," a fictionalized take on the real-life Edward "Ned" Kynaston.

For Ned, who made a name for himself playing Shakespeare's great ladies, the fantasy, the effect, is everything. He revels in the confusion his pretty appearance causes his fans, and he refuses to meet with them unless he is in full stage regalia. "They want the illusion," he says, "not some green-room hermaphrodite."

Ned (Billy Crudup) is attended to by his adoring dresser, Maria (Claire Danes), who watches him from the wings, longing to be in his place. When a love-whipped King Charles II (Rupert Everett) is swayed by the buxom, brainy and stage-hungry Nell Gwynn to ban male actors from playing women, Maria's wish is granted. Suddenly she is in her employer's place, the star of stage. And Ned is, just as suddenly, without a role.

In the hands of Richard Eyre -- director of screen (the delicate yet unsentimental "Iris") and stage (the Tony-nominated revival of "The Crucible") -- "Stage Beauty" is a comedy in the classic sense, that is, in the all's-well-that-ends-well sense, where the cross-dresser gets the girl and everyone rides happily off into the sunset.

A few spots that telegraph loudly as plot devices (such as when the self-assured Maria spirals into self-doubt, bringing Ned rushing to her aid) are minor sins easily forgiven in the rush of biting dialogue, snappy pace and a wink-wink approach to sexuality and gender-bending. Yet what keeps "Stage Beauty" from being merely delightful froth is Ned's story and the vanity and pathos that Crudup brings to it. As the cast-aside Ned, Crudup embodies a man without moorings, longing for the old days, when his training -- actors studied feminine wiles for years before being allowed to put on a dress -- meant something. Women do everything beautifully, he tells Maria, men feel too much. Feeling ruins the effect.

From "Stage Beauty" you can infer all sorts of metaphors and big themes about the role of men and women, about the nature of love and sexuality. And perhaps you wouldn't be far off.

But ultimately this is a celebration of the theater, a big, wet kiss to the craft of acting and the artists who inhabited London's early stages. It's fascinating to watch the metamorphosis from the highly stylized formality, not to mention sexism, of Elizabethan theater -- that is, the five positions of feminine subjugation -- to a more naturalistic approach that presaged modern theater, where raw emotion leaves audiences literally on the edge of their seats.

To watch Crudup and Danes (off-screen lovers with a somewhat scandalous backstory of their own) play Ned and Maria playing Othello and Desdemona is to see the play, and a movie, brought to thrillingly vivid and haunting life.

Stage Beauty (105 minutes, at area theaters) is rated R for bawdy, sexual themes, brief nudity and profanity.

In "Stage Beauty," former dresser Maria (Claire Danes) takes it upon herself to help Ned (Billy Crudup) after he is no longer allowed to play women's roles.