Klavdia, the heroine of the new Soviet film "Lonely Woman Seeks Life Companion," is a woman of shadows. From the moment we first see her, standing in the hallway of her Moscow flat, her face half in darkness, she appears haunted and half-crazy from neglect. As the movie opens, she's just come in after running through the streets in the rain putting up ads asking for single men to contact her, and the desperation of the act -- no personals ads are published in Soviet newspapers -- seems to have made her even more depressed. With her pallid, bone-china complexion, she's not unattractive, but there's no lightness in her, no romance. It's fitting that she's advertised for a lover because she's all business. Misery seems to have incinerated her spirit. Her eyes burn with sorrow.

The film, directed by Viacheslav Krishtofovich, is a study in despair, and if it didn't have such a vivid performance at its center it might be oppressively bleak, a gray-out. But with the great Soviet actress Irina Kupchenko as Klavdia, it becomes just the opposite, a scintillatingly corrosive descent into hopelessness.

Kupchenko delivers her character's anguish with bell-like clarity; this is a crystalline performance, and all the more remarkable because the woman she plays is not delicate in the least. When a man appears at her door in response to her note, she eyes him with suspicion and immediately dismisses him as unsuitable. Despite the fact that she bonks him on the head with an ironing board, her suitor, Valentin (Alexander Zbruyev), a homeless former circus acrobat living on a meager disability pension, doesn't give up. His doggedness, in fact, touches her, and though she finally begins to respond to him, buying him clothes and even allowing him to sleep in her kitchen, she can't bring herself to accept his obviously well-meaning attention.

It's this back-and-forth game of emotional tennis that makes "Lonely Woman" so penetrating. Klavdia and Valentin are virtually the only characters in the film, most of which takes place in Klavdia's cramped apartment. And most often the camera focuses on their faces, capturing the flickers of emotion that pass between them. Krishtofovich keeps the story simple; his style is the most relaxed variety of naturalism imaginable. But because of the brilliance of the actors -- three or four different shifts of temperament flash underneath each line-reading -- there's enormous complexity within this simplicity.

Western audiences, in fact, may not be used to this kind of purity and concentration and may mistake the characters' malaise -- which Krishtofovich connects with the general grayness of Soviet life -- as drabness. They may miss the fires smoldering beneath the actors' subtlety.

It's impossible, though, not to be tortured by the sight of this blighted woman, especially when she rages against a friend of Valentin who urges her to save him. "I don't want to save anyone," she cries. "I want to be saved." This is the call of a ravaged soul, and Kupchenko inhabits its pain completely. This is fierce, unflinching acting. I doubt that any other performance this year will match its dark, moving savagery.

Lonely Woman Seeks Life Companion, at the Key, is unrated.