Then she sings. Boy, does she ever. From that elastic mouth comes the smoky soul of Bassey, the round tones of Garland, the breathy coo of Monroe. In fact, we hear Little Voice's dead-on impersonations before we hear her speech -- which, true to her name, she ekes out in a tremulous bleat. And Horrocks doesn't lip-synch a note. Balancing eccentricity with fragile emotion, it's the performance of a consummate character actor.

Horrocks, who was last seen stateside as the flamboyant publicist Bubble in the Absolutely Fabulous series, originated the agoraphobic songbird in the hit London play The Rise and Fall of Little Voice. Set in a somber seaside town in Northern England, this adaptation opens up the production for the big screen. Little Voice, however, still spends most of her time in her attic bedroom, where she escapes the nonstop cackling of her pub-floozie mum, Mari (Secrets & Lies' Brenda Blethyn), by singing along to her dead father's record collection. Talk about "My Heart Belongs to Daddy": in the film's hokier moments, the apparition of dear old dad actually appears to smile upon his daughter's sensual warblings.

Little Voice's amazing gifts, of course, can't remain a secret, and it's not long before her songs beguile the ear of washed-up talent scout Ray Say (Michael Caine), who stumbles home with the love-starved Mari for a little slap and tickle. But what he hears in Little Voice's music isn't just beauty, it's bounty -- heaps of money -- and he risks everything to make her private songs a public spectacle.

It's to Horrocks's credit that her performance isn't drowned out by her formidable -- and raucous -- supporting cast. Blethyn, all crepey cleavage and caked-on make-up, lurches into shrill monstrosity; with her Eliza Doolittle inflection and volume-11 delivery, she starts out as farcical but simply becomes too much. And for those who ever wondered what Alfie moldered into, wonder no more. Caine, his golden curls slicked, a medallion at his throat, turns in a performance of tour de force proportions, an Aqua Velva'd self-parody that's as sentimental as it is smarmy. Completely lost in the cacophony is a miscast Ewan McGregor, who with plastered hair and earnest gaze plays against type as a pigeon-keeping telephone repairman smitten with Little Voice. In a film already feathered with too many avian motifs -- its canary-like star, a rendition of "Come Fly with Me," a lot of talk comparing life to "soaring" -- McGregor flaps about unmemorably.

Like The Full Monty and Herman's previous effort, Brassed Off, Little Voice uncovers its most bittersweet laughs in the wayward dreams of working-class folk. Here the best errant aspirations are housed at Mr. Boo's, the seedy nightclub where Ray and the establishment's titular owner (a deliciously bleary-eyed Jim Broadbent) hope to unveil Little Voice. It's desperation of the laugh-or-cry variety, and Herman deftly locates the amusing, self-reflexive absurdity in what passes for entertainment.

In its quest for broad humor, the film isn't above taking a cheap shot or two. Especially vulnerable are the fleshy forms of Blethyn and Annette Badland, who plays Sadie, Mari's best friend. In one scene, the pair celebrate Mari's relationship with Ray by boogieing about the house; Mari jiggles her bosom as the obese Sadie grinds against a creaking banister before toppling the couch. Another scene finds Sadie snorting à la Babe.

So Little Voice loses its way at points, especially in its hurried, portentous ending. Yet it never obscures the blinding talent of Horrocks. Her climactic performance is nothing short of mesmerizing, and her ability to channel music's great divas never feels like shtick. It's actually moving. A funny, wistful allegory about the whims of self-expression, Little Voice promises Horrocks a big future.