'One Day' delves into two lives

What a difference a day makes.

Some are memorable for reasons that become clear in retrospect. Such is the case for Dexter and Emma, the central couple in the surprisingly profound One Day.

David Nicholls wrote the witty prose of the best-selling novel and the deftly constructed screenplay, and the central concept, so absorbing as a literary device, translates surprisingly well to the screen.

The story begins on July 15, 1988, graduation day for Emma Morley (Anne Hathaway) and Dexter Mayhew (Jim Sturgess), Edinburgh college students who skirt a one-night hookup and begin a life-long friendship. As the saga spans 1988 to 2011, the story checks in yearly with the characters on the same calendar day to gauge where their lives have taken them. Often, it's not very far. The core conceit is employed subtly, never resorts to gimmickry and spares audiences thudding swaths of exposition.

Amid sharp banter, the film poignantly captures how lives meander and take unexpected turns. Intellectual promise doesn't always lead to a brilliant career, and jobs that seem glamorous often go nowhere.

Emma labors for a couple years as a waitress in London, though she has obvious writing talent. Dexter is a TV presenter who affects a party-hearty manner that irritates most of Britain.

The inspired casting of Hathaway and Sturgess makes the story all the more emotionally engaging.

As the whip-smart, drily funny Emma, Hathaway is terrific. The actress nails the working-class character down to the idiosyncrasies of her North England accent. Her initial gawky charm is conveyed believably, as is her graceful transformation into a successful writer. Hathaway's self-deprecating grimace speaks volumes about Emma's shaky confidence.

Dexter takes longer to mature and shed his self-absorption. Sturgess conveys the various facets of his character superbly. He goes from casually charming college heartthrob to slick on-camera personality to rudderless wash-up and eventually to loving father. He has a more dramatic arc than Emma, but Emma is more consistently sympathetic.

Several supporting characters are excellent, particularly Rafe Spall as Ian, the awkward, unfunny stand-up comedian besotted with Emma.

Director Lone Scherfig was a wise choice for the material. Her last film, 2009's An Education, demonstrated her clear-eyed style and ease with complex material.

One Day is an aching lovely romance, but it's also an insightful look at human potential and the search for a purposeful existence.