Philosophically provocative and achingly sad, "Never Let Me Go" manages to touch the mind and the heart at once, and with equal measure.

Longtime video director Mark Romanek, whose last feature was the haunting "One Hour Photo" from 2002, has made a film that's sumptuously gorgeous and filled with sterling performances. The textures, the lighting - everything is carefully crafted but never stuffy, and, at times, even a little gritty in an appealing way.

But, based on the novel by acclaimed "Remains of the Day" author Kazuo Ishiguro, "Never Let Me Go" also raises intriguing questions about medical ethics and the nature of humanity itself. Some may find its tone suffocatingly heavy, and the score can feel a bit melodramatic and intrusive here and there. But if you give into it, you'll find yourself sucked into this melancholy alternate world, an ambitious hybrid of sci-fi drama and coming-of-age romance set in a British boarding school.

That's where the tale begins in the late '70s, at the exclusive Hailsham, where headmistress Miss Emily (Charlotte Rampling) reminds the children they're special in a tone so stern and full of conviction, it almost sounds as if she's scolding rather than encouraging them.

Prime among the students are Kathy, Tommy and Ruth, whose tentative love triangle at age 11 will form the film's dramatic arc. Young actors Isobel Meikle-Small, Charlie Rowe and Ella Purnell are all so natural and excellently cast, they actually make the relationship more compelling at this age than the actors who will go on to portray the characters as adults. That's no small feat, given we're talking about Carey Mulligan, Andrew Garfield and Keira Knightley.

In adapting Ishiguro's book, screenwriter Alex Garland ("28 Days Later") reveals the mystery of the children's unusual existence slowly and suspensefully, through details and gestures that are small and spare. We know something's different about them: their fear of leaving the school grounds, the daily pills and bottles of milk lined up for them to consume, the bracelets that monitor their comings and goings. But only after a new teacher arrives, played with subtlety and sympathy by Sally Hawkins, do we (and they) learn their true purpose.

Quiet, bookish Kathy and raging, impulsive Tommy may seem like unlikely friends, but as they look out for each, they realize they're probably also soul mates. Ruth inserts herself between them out of jealousy, the need to be wanted, who knows? But she tears the two apart, and keeps them apart almost permanently.

"Never Let Me Go" then jumps ahead seven years, to when they're all 18 and have left school, but they're still living a sheltered life. Only then do they begin to show a curiosity about the outside world, and their hesitant interactions with others provide the film's few glimmers of humor. Jumping ahead nine more years reveals the fate that was waiting for them all along, when words such as "carer," "donation" and "completion" sadly make more sense.

Rated R for some sexuality and nudity.

'Never Let Me Go'

Starring Keira Knightley, Carey Mulligan and Andrew Garfield. Directed by Mark Romanek. Rated R (103 minutes).