Vera Drake, a middle-aged housecleaner in 1950s London, likes to hum a happy tune while she works. Unfailingly chipper in her frumpy dress and well-worn apron, she tackles each day's tasks with a determined smile and warm blue eyes, whether she's polishing the brass of the well-to-do, caring for an invalid neighbor in between stops, or cooking for her family when the long day is over. In fact, even when she secretly sneaks to That Other Job -- performing illegal abortions in the dank apartments of desperate lower-class women -- Vera offers up a post-procedure cup of tea with a spoonful of plucky.

Sweet, strange and ultimately heartbreaking, "Vera Drake" is another slice of British proletarian life from director Mike Leigh ("Secrets & Lies"), an auteur who encourages improvisation from his actors and often keeps vital plot points from them to better capture genuine reactions. Leigh's a realist for sure, and yet Vera, played by the subtly mesmerizing Imelda Staunton (who's justifiably scooping up film festival awards for her work), behaves as if she's in another film altogether. Say, David Lynch's "Mary Poppins."

Leigh's movie is fiction, but it's certainly not fantasy. Vera's surroundings are bleak, filled with long shadows, ramshackle rowhouses and poor lost souls, including her emotionally stunted daughter, Ethel (the disturbing Alex Kelly), and a simple, doughy-faced man (the even more disturbing Eddie Marsan) vying to be the homely girl's suitor. Vera's husband, Stan (Phil Davis), works as a mechanic in his brother's garage, but behind his sturdy facade is a man beset by worry about making ends meet. Without the support of his wife, he'd be lost. (Daniel Mays, as Vera's son, adds to the Lynchian vibe with his pinched face and "Eraserhead"-high hair.)

Leigh sets Vera's regular daily chores to a spare, chilly piano soundtrack, but each time she unveils the rudimentary supplies of her dark art -- including a cheese grater, carbolic soap and a Higginson syringe (that is, a colon tube with a squeeze bulb) -- silence prevails. The abortion scenes aren't overly graphic, but they are hard to watch, as the women tremble and Vera softly chirps bedside instruction. "You go all floppy for me," she says, hushing a girl who won't sit still.

Unveiling the story with a slow, restrained pace, Leigh forgoes moralizing and taking sides. The money-minded woman who gives Vera her assignments (Ruth Sheen) is as cartoonishly eeevil and greedy as Vera is Disney-sweet. (Vera is unaware that the women are being charged for the service.) The director also weaves in a subplot involving how the Other Half handles the taboo topic of unwanted pregnancies (claims of "emotional distress," real doctors, clean surroundings), but the resultant emotional wallop is portrayed as equal for both rich and poor.

After a young woman is rushed to the hospital after an appointment with Vera, the film's heroine (anti-heroine?) is ratted out, and the rest of the Drake family -- who have all been kept in the dark about Vera's freelancing -- watch dumbfounded as mom, wife, leader of the brood is taken from her home by the police. What could this dear, sweet homemaker have done?

Staunton's transformation in the film's final act is nothing short of astounding: Her hair a mess, her face streaked with tears, Vera sits in a police interrogation room, motionless for perhaps the first time in her life. Her smile has vanished, her eyes are empty, her face is slack with confusion. The fact that she has injured someone is just not processing. When asked by the police -- visibly uncomfortable with grilling a woman who might as well be their mother -- how many abortions she's performed, she opens her mouth but no words come out. Leigh lingers on Staunton for prolonged stretches, and when the director eventually cuts to frantic hubby Stan pacing unawares in the station lobby, that change of scenery offers no relief, either.

The film, a small but powerful character study first and foremost, closes with a trial, but Vera's fate has been sealed long before the verdict comes in. Played by the remarkable Staunton, she's a woman who's ultimately felled by her greatest strength: the goodness of her own blind heart.

Vera Drake (120 minutes, at area theaters) is rated R for depiction of strong thematic material.

Imelda Staunton plays Vera Drake, a housecleaner who performs illegal abortions for poor women in 1950s London.