It’s all laughably ridiculous, of course, the entire concept behind the romantic comedy-drama One Day. The part of me that can’t help nitpicking logical absurdities — that song on the radio in that scene set in July 1995 didn’t come out until August 1995! — realizes that the significance July 15 takes on in the relationship between the story’s protagonists would make an astrologer incredulous. Arms should fold, heads should shake: Nope. No way. No how.

So maybe there’s no logical way to defend the way One Day charmed me. As adapted by David Nicholls from his popular tear-jerking novel, it’s hardly an example of clockwork plotting. It simply does much of what you ask of a romance: It gives you two interesting people and a reason to hope that they wind up happy.

The chronological story begins on July 15, 1988, when a bunch of young Brits are celebrating their college graduation. Among them are Emma Morley (Anne Hathaway) and Dex Mayhew (Jim Sturgess), who have known each other casually through mutual friends but take the opportunity of their revelry for an equally casual hook-up — almost. While their evening isn’t quite consummated, Emma and Dex resolve to remain good friends. And over the course of more than 20 years, we revisit them every July 15 to see how that friendship is working out, through career, geographical, and relationship shifts that test the bond between them.

What we’ve got is essentially a slightly more melancholy version of When Harry Met Sally, a decades-spanning tale of two best friends who need to have fate knock their heads together before they can figure out whether they’re perfect for each other. Naturally, there are a variety of impediments. Often they’re in different countries; Emma begins a long-term relationship with a would-be stand-up comedian (Rafe Spall); Dex gets married to a woman he gets pregnant (Romola Garai); and perhaps most significantly, Dex becomes a popular TV personality hosting vapid variety shows, transforming into an alcoholic, addict, and general dickhead in the process.

Yet somehow their worlds almost always manage to intersect on St. Swithin’s Day, metaphorically significant, perhaps, for an old British rhyme about the summer weather, making it something of a Groundhog Day for portending things to come. July 15 marks not only the day that their friendship first blossoms, but a day for weddings, announcing future weddings, having critical fights, confessing their mutual feelings at last, and … well, a few other significant things. While some of the events could certainly be attributed to the sentimental resonance of the date on future decisions, Nicholls pushes it just for the sake of a gimmick. If he just wants to tell the story of a relationship, the same-day device is unnecessary; if he wants to provide a snapshot of how a relationship looks on the same day every year, he’s cheating.

Despite the cheating, though, One Day works for that most fundamental, oft-ignored of reasons: affection for the characters. Hathaway continues emerging as a genuine acting force, allowing Emma’s growing self-confidence to permeate every subsequent interaction with Dex. She’s a heroine infinitely worth rooting for. And while Dex muddles through a stretch of obnoxiousness and self-pity, Sturgess finds something basically decent in his desire to maintain his friendship with Emma. Nicholls and director Lone Scherfig (An Education) keep the tone light and frisky throughout much of the first hour, allowing the charming chemistry to build between the two leads so that the story’s more serious turns are built on a foundation that keeps them from feeling exploitative.

The plot takes a few mawkish turns in its third act, but One Day may save its smartest decision for last, as the narrative reverses course to show us the day after July 15, 1988, the only non-July 15 day the film ever shows us. Not only does it showcase the characters at their most endearing and vulnerable, at a pivotal moment when the connection between them could head in one of two very different directions, but it escapes the gimmick enough to show us that all the other days between Emma and Dex were just as important in their lives. That’s the way you get a cynical, arms-folded critic to suspend disbelief: Build a relationship strong enough that I start to care about all those other days.

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