WILLIAM FABER (Fabrice Luchini), a shy, primly dressed tax consultant, sits stunned as the woman (Sandrine Bonnaire) sitting across his desk unloads her personal problems. Although his clients often involve him in such matters, this woman is really talking intimately. Faber quickly realizes his visitor, whom he later learns is Anna, has probably confused him for the psychiatrist (Michel Duchaussoy) who works down the hall.

Patrice Leconte's assured and deeply involving "Intimate Strangers" is about the reasons behind our reasons. William knows it's just a matter of telling Anna she's got the wrong guy. But there's something about this woman -- and take one look at Bonnaire in this movie and you'll need no explanation -- that makes him unable to send her away. After that first "session," Anna is gone before William can even recover. And already he knows that her marriage is in trouble and that her husband and she have not had sex in six months.

She's not just attractive, she's direct, vulnerable and she needs him. She has chosen him. William Faber, that is. A lonely Parisian whose girlfriend Jeanne (Anne Brochet) has left him for a bodybuilder. Who keeps his childhood toys in tidy formations around his office. Who has lived and worked in that building all his life. Who inherited this office from his father. William Faber, who needs a romantic explosion in his cold, dead life.

It's the beginning of a strange, intoxicating relationship, much to the chagrin of William's secretary, Madame Mulon (Helene Surgere). And even when Anna realizes William isn't the analyst she thought, and chastises him for playing along, she continues the relationship. After all, she needs him. She claims her emotionally distraught husband, who has lost his job and his ability to sexually perform, has told Anna to find a stranger and have an affair. It's her husband's way of arousing himself, apparently.

When she doesn't show up for an "appointment," William is worried. He goes in desperation to the shrink that Anna presumably was looking for in the first place, and instead finds himself sitting down as an unintentional patient with the wily Dr. Monnier. Who's the crazy one here?

Luchini shows why he has been a lasting staple of modern French cinema. As the bottled-up William, he's the emotional center. He has a particularly glistening stare that tells you about vulnerability, pent-up desires and a frazzled intelligence. And to see him boogie in the privacy of his own apartment to a recording of "In the Midnight Hour" is an amazing mixture of comedy and poignancy. Bonnaire, another Gallic icon herself, justifies William's intensity with effortless grace. And no one has smoked a cigarette like that in recent memory.

For a movie that spends most of its time in William's office, this is remarkably entertaining. You never feel cooped up. In films such as "Monsieur Hire" and "L'Homme du Train" ("Man on the Train"), writer-director Leconte has already displayed his genius for the unfolding of character, the sheer magic of two people discovering things about each other, quirky nuance by nuance. "Intimate Strangers" (Leconte's 20th feature film) takes us from that initial, mistaken-identity encounter to an ever-deepening discovery of William and Anna. And around them, Leconte introduces us to some wonderful supporting characters. Madame Mulon is a quiet, fussy riot as William's long-suffering secretary, who watches, appalled and eventually moved, as William turns from geeky taxman to a soul consumed with newfound passion. Dr. Monnier, too, is a corker, a man who never misses a chance to pontificate or charge by the hour.

This is the kind of sophisticated and pleasurable movie you dream of seeing from France. But unfortunately, Leconte claims this is the last of his films dealing with adult, romantic themes. So grab this opportunity to see "Intimate Strangers," or expect to wait a long time for something half as smart and enjoyable.

INTIMATE STRANGERS (Confidences Trop Intimes) (R, 105 minutes) -- Contains frank sexual conversation and sexual situations. In French with subtitles. At Landmark's E Street Cinema, Cineplex Odeon Shirlington and Cinema Arts Fairfax.

Sandrine Bonnaire in "Intimate Strangers," another smart, sexy, sophisticated exploration of desire from French master Patrice Leconte.