Like a briny chorus trilling, "I've Heard the Mermaids Singing" provides a soaring anthem to the world's unsung. Flighty as a sea horse and likewise unfettered, this first feature by Canadian Patricia Rozema finds inspiration in J. Alfred Prufrock's sad quatrain. But unlike T.S. Eliot's poor, jaded Prufrock, Rozema's unsure heroine listens when the sirens sing. And that is the lovely notion behind this captivating comedy-on-a-shoestring.

This evocative character study depicts a young artist's infatuation and later disenchantment with a pretentious art dealer, an affair of the mind that causes her to come of age. It won the Prix de la Jeunesse this year at Cannes, and like 1986's winner, "She's Gotta Have It," Rozema's work is rough around the edges, brimming with uncontrolled talent and confiding as a close friend. And like its protagonist Polly Vandersma, it is not as simple-minded as it first seems, for under all the whimsy, an allegory hides.

Polly's story, which expands on the themes of Rozema's short work "Passion: A Letter in 16 MM," begins as a confession, eyeball to eyeball with the audience. It is an assault on the fourth wall, with the camera squirming to keep up with Polly. It's an immediately engaging technique eminently suited to Sheila McCarthy, the fey leading lady.

This accomplished comedian, a Canadian stage veteran, looks like some inspired cross between Raggedy Ann and Liza Minnelli. Her carrot-colored hair sticks up in tufts like worn shag; her eyes, big as yo-yos, are expressive as a cocker spaniel's. When confronted with chopsticks and a plateful of raw octopus, she plays the scene as Chaplin might have, all social ineptitude and clowning grace.

Polly is a modern-day waif who lives through her photography. Though "organizationally impaired," she becomes a secretary to the worldly art snob Gabrielle St.-Peres, whom Polly worships as the Curator. Paule Baillargeon plays this chilly icon, who becomes the Art God in Polly's wide eyes.

The Curator is all things artsy-smartsy, but to Polly, infatuated with her elegance, pseudo-intelligence and slight French accent, "she was like a fairy tale ... She said things like 'His work shows acute awareness.' At first, I thought she meant like a cute face." Polly, hoping to win the Curator's approval, sends her collection of photographs to her under a "pseudo name." Gabrielle dismisses them instantly, and Polly is crushed, although she emerges the wiser for the rejection.

When she picks up a camera, the sirens sing their irresistible song. Her photographs send her into darkroom reveries in which she climbs skyscrapers, soars like Superman and engages the Curator in brilliant conversation. Rozema is depicting a democracy of the Muses; they are as apt to inspire Polly, or Rozema, as Pablo Picasso. And Rozema's script fairly skips along.

She builds a bittersweet story of self-discovery: Polly's joy in her art is diminished when she seeks outside validation from Gabrielle. Mermaids will not even hum for the likes of the Curator, though they do bless Rozema's pure intentions.

I've Heard the Mermaids Singing, at the Key, is unrated.