"I'VE HEARD The Mermaids Singing" is a serenade to the world's meek and mousy -- and the demure, the unassuming and the softspoken. Writer/director Patricia Rozema's delicate peek at wallflower Polly Vandersma is a delightful mix of fable and passion play, with the gritty, "She's Gotta Have It" appeal.

Polly (played with cuddly duckling panache by Sheila McCarthy) is all kid-glove feelings and unpretentiousness. Speaking into a video camera Woody-Allen style, she talks about her small life in a "bachelorette" apartment with only the photographs she constantly takes as decoration. Temp agencies have labeled her "organizationally impaired." She winces at herself. Her only release from this modest life is occasional flights of fancy (in which she actually flies, sort of), her camera and this new boss she's impressed with.

That boss being Gabrielle St. Pe`res (Paule Baillargeon), the oh-so-'teric museum curator who gains Polly's unabashed admiration -- first of all by hiring her, but mostly by her ability to engage in Artspeak with such phrases as "oblique pragmatism." Even after discovering Gabrielle's past affair with a woman artist (in a nice scene involving the museum's video monitor), the adulation continues.

Drunk and feeling confessional one night, Gabrielle admits a burning need to be an artist. And when she pulls out some old paintings, Polly is overwhelmed and determined to help out. She surreptitiously shows one work to an art critic, who then heralds it to the world -- making Gabrielle the instant talk of the town.

Polly will, however, discover disturbing truths about Gabrielle, and after Gabrielle disparages Polly's photographs (not knowing whose pictures they are), Polly's disappointment is resounding. Things get rather serious and perhaps a little too contrived. But by this time we're hooked -- this overall feeling aided by Douglas Koch's imaginative cinematography, Rozema's light mullings on God and creation, Mark Koven's punky-tronic score and, above all, Sheila McCarthy's Polly -- petrified by her octopus dish at a sushi restaurant but able later to confront authority. The victory Polly celebrates in the end wouldn't rate more than a passing diary entry in anyone else's life. But for Polly, it's a triumph at Waterloo.

I'VE HEARD THE MERMAIDS SINGING (Unrated) --

At the Key.