An Education opens Friday in select theaters

Sex and love is the great subject of movies, but compelling treatments of it are relatively rare. Great romantic filmsAlfred Hitchcock’s Notorious and David Lean’s Brief Encounter are a couple of the bestare able to convey the terrible melancholy of heartache and the dizzying ecstasy of falling in love. Lone Scherfig’s An Education isn’t quite a great movie, but for about half of its running time it effectively sweeps us along as a teenage girl makes dangerous choices that are completely understandable in the emotional context of the film.

The film is set in London in 1961. The date is important: Swinging London has yet to arrive. Jenny (Carey Mulligan) is a bright, brave-spirited 16-year-old, an only child from a suburban family. Her obtuse (and, as played by Alfred Molina, hilarious) father obsesses about money, but he and Jenny’s mother (Cara Seymour) are determined to see her make it to Oxford. Jenny plays the cello and speaks French; a nice boy in her orchestra has a crush on her. It’s not an exciting life, but her prospects are good and her favorite teacher, Miss Stubbs (Olivia Williams), has high hopes for her. There’s little doubt that Jenny will ace her A-levels and move on to the adult world she’s more than ready for.

And along comes David (Peter Sarsgaard), a well-dressed, well-spoken man in his 30s. It is written that boys and girls must meet cute in the movies, and screenwriter Nick Hornby (High Fidelity, Fever Pitch), working from a brief, apparently bitter memoir by journalist Lynn Barber, obliges. Jenny is waiting in the rain for a bus, and David pulls up alongside in his Bristol roadster. He knows Jenny isn’t reckless enough to get into a car with a male stranger, but he tells her that, as a classical music fan, he cannot allow her cello to get wet. So her cello goes into his car, and she walks alongside as he drives slowly along. It’s a marvelously executed scene that’s utterly crucial to our investment in the film: We have to appreciate, if not support, this flirtation between a grown man and a teenage girl if we’re going to enjoy the film.

We discover that David is Jewish, an outsider in the still quite anti-Semitic Britain of the day, and to Jenny he’s a kindred spirit, a man who understands her yearnings and who apparently has the means to bring her into his world of black-tie Ravel recitals, fine-art auctions and outré entertainments, like dog tracks. Jenny is smitten, too, with David’s friend Danny (Dominic Cooper) and his good-natured bimbo girlfriend, Helen (an amusing Rosamund Pike). Jenny’s new friends turn out to have a sinisterbut still seductiveside, but until she begins to see things clearly, she’s swept up in the culture, clothes and apparent liberty of her new world.

Mulligan, who was about 22 years old at the time of filming, is credible as a teenager and even more so during her whirlwind romance with David, when she’s made over into Audrey Hepburn-esque glory. However, Sarsgaard is the film’s linchpin. We have to empathize with his needs on some level, and he does a fine job of convincing us that no, he’s not a perv, even if he is guilty of other bad things.

Throughout, the film’s wit is impressiveMolina’s enunciation of the words “Teddy boy” is a howler, and I especially liked the treatment of the character of Graham (Matthew Beard), Jenny’s age-appropriate and appealing suitor who doesn’t stand a chance against David’s superior resources.

What makes this film so watchablein addition to Hornby’s reliably pungent dialogueis that it effectively captures the delirium of amour fou. The romance is so wrong, but it provides such a rush that we understand why the characters plow ahead. Where the film falls short, however, is when it slips into comfortable moralizing that seems more befitting of the safe suburban world that Jenny wants to escape. The film is happy to embrace the stylings of the hip leading edge of the 1960s, but the morality of this movie is 1950s. In this movie, lovers have to say they’re sorry.