Carey Mulligan in Folk Musical

Nostalgia and the ache of moving on permeate every frame of The Ballad of Wallis Island, lending an air of precious sentimentality that threatens to slide into the saccharine. But James Griffiths’ tender comedy-drama also has a ton of heart, a generosity of spirit and an ultimately disarming sweetness that make it sneak up on you, cynicism be damned. It’s also quite funny, in an eccentric, decidedly British way that you either tap into or you don’t. Imagine John Carney’s Once plonked down in the middle of a reluctant buddy movie about finding hope in loss and you’re halfway there.

There’s probably no way to describe the film without making it sound twee. But the performances are so lived-in that what could have been an overdose of whimsy instead acquires emotional substance in its reflections on life, above all on accepting the sadness and regrets of the past and finding a forward path. Like the characters, the setting is also fully inhabited, though sparsely populated — a picturesque Welsh coastal town standing in for the fictitious island of the title.

That island is the sleepy spot where established music star Herb McGwyer (Tom Basden) arrives by rowboat for a lucrative gig, annoyed to find there’s neither a harbor nor even a wharf and he’ll have to wade in to shore. As arrivals go, it’s a disaster. He falls into the water, putting his cellphone out of commission and worsening his already sour mood. He’s further underwhelmed to find there’s no hotel on the island; he’ll be staying with the irritatingly cheery chap who serves as his one-man welcoming party on the beach.

“Can’t they send a car?” asks Herb with a hilarious sense of privilege, despite there being no road in sight, as they trudge up the winding muddy path to the house. Herb hasn’t yet realized that they begins and ends with his host, Charles (Tim Key).

As peevish and spiky as Herb is, his sarcastic grumbling appears to bounce right off Charles, who never met a groan-worthy pun (apologies to Judi Dench and Winona Ryder) or a silly bit of wordplay he didn’t love. The widower is a two-time National Lottery winner who lives an uncomplicated existence in an old mansion both grand and shabby. He seldom stops talking, but a look in his eyes during his fleeting moments of silence suggests that underneath all the jovial banter is a man yearning for connection.

Charles’ devotion to the soulful folk-rock and delicate harmonies of McGwyer Mortimer is almost religious. The duo’s popularity peaked in 2014, not long before the acrimonious split of the creative collaborators and romantic partners. Herb has agreed to Charles’ proposal to play a single acoustic concert on Wallis Island before an audience of “less than 100,” for which he will receive the princely sum of half a million pounds.

Herb thinks Charles is a superfan nutjob. “I’m in Misery, I’m going to wake up with no ankles,” he tells his manager from the payphone outside the local shop.  What Charles hasn’t told him is that he has also invited Nell Mortimer (Carey Mulligan), the other half of the defunct duo. One more detail he has kept quiet is that the show will be for an audience of just one.

The awkward reunion between Herb and Nell after nine years of estrangement is made even more uncomfortable when she arrives with her American husband Michael (Akemnji Ndifornyen).

While Herb has remained in the music business as a solo artist, veering into unfulfilling commercial pop and “collabs” with younger stars to keep him relevant, Nell has left all that behind. She seems content with her life in Portland, Oregon, making chutney to sell at the local farmers’ market. But it turns out that both McGwyer and Mortimer need the money.

Basden and Key’s screenplay — fleshed out from their 2007 short, The One and Only Herb McGwyer Plays Wallis Island — is a bit contrived in its method of getting Michael out of the picture, making him a birdwatching enthusiast and sending him off on a tour to the other side of the island in search of puffins.

Herb is initially reluctant to dip into the McGwyer Mortimer back-catalogue, which clearly has associations with a time he’d rather not revisit. Nell is more relaxed than her tightly wound former partner. The first time they sing together as they begin rehearsals is magical, making it appropriate that Charles is speechless, for just a moment, before returning to his default verbose setting. The tender feelings playing across his face point to his own bittersweet associations with the music.

While the duo’s songs are heard on Charles’ turntable from the start, the first time we see them performing together kicks the movie’s poignancy up several notches. Basden wrote the songs, which are tuneful and pleasing to the ear, even if it’s the window they provide into Herb and Nell’s past that makes them so stirring. The actors sound lovely together, with the warmth of two people who have a history, etched deep enough to make the good stuff count, even if it eventually curdled.

Herb and Nell both seem impressed, even touched, by the level of Charles’ fandom. In addition to their albums, he has extensive press clippings that include an NME cover story, plus gig posters and even their old guitars bought at auction. While it’s spoken of only briefly, his adoration for vintage McGwyer Mortimer is clearly a way of keeping alive the memory of his late wife, who was an even bigger fan.

The intimacy of their duets stirs up something in Herb that he swept under the rug years ago, while Nell still bristles at the slap of him going off to record a solo album without telling her. But there are no blow-up fights, just meaningful conversations.

While the movie occasionally gets sugary, one of the things that distinguishes the screenplay is its refusal to take expected routes or get trapped into clichéd corners. It’s never a “will they or won’t they get back together?” scenario, even as Herb insists that the feelings between them are still there. It’s more about what the music does for Charles, and in turn, what the experience ultimately does for Herb, when he’s not attempting to bail on the whole idea and get out of there. Which is easier said than done with such an erratic boat service.

Mulligan brings luminous self-possession to her supporting role, which recalls her appearance as another folk singer in the Coens’ instant classic Inside Llewyn Davis. There’s a softness to Nell but also a sharp edge here and there as she remains firmly grounded and resistant to the notion of the duo reforming professionally.

The movie fundamentally is an odd-couple love story (can we please retire the term “bromance?”) between Herb and Charles. Basden, who has an angular, lanky David Tennant look and a terrific handle on snarky delivery, can barely tolerate Charles for much of the action and seems to be only half-joking when he mentions taking out a restraining order after the gig. But Charles’ infectious passion for McGwyer Mortimer’s music prompts Herb to be honest with himself about how far his output has strayed from his authentic voice.

Basden and Key have worked together in comedy since the early 2000s. That familiarity shows in their rapport, whether it’s Herb’s tetchy eye-rolling at Charles’ nonstop prattle or the rare quiet moments in which the empty spaces in their lives give them common ground. Basden plays the deadpan straight man and Key is the clown with a bruised heart, equal parts annoying and endearing.

Charles also gets more than just a special occasion to honor his wife. He gets the nerve to address the loneliness he’s been hiding behind dad jokes and put himself out there again. With a nudge first from Nell and then more forcefully from Herb, that means acknowledging his attraction to the shopkeeper Amanda, and maybe even acting on it.

Amanda is played by the wonderful Sian Clifford, who’s as easygoing and kind here as she was sublimely acerbic and tense in Fleabag, as the Pheobe Waller-Bridge character’s sister, Claire. (God, I miss that show.) Amanda isn’t the best at keeping all the right groceries in stock, but like Nell, she seems to have figured out life.

Griffiths — a seasoned TV director on shows like Black-ish, A Million Little Things and Bad Sisters, who also directed the original short film — keeps things agreeably simple, focusing on the characters and giving the actors space to explore affecting depths in their feelings. Cinematographer G. Magni Ágústsson’s visuals take full advantage of the physical beauty and natural light of the location, without resorting to postcard prettiness.

The Ballad of Wallis Island breaks no new ground, but it’s an unexpectedly pleasurable, funny-sad watch, full of sweet, soothing music.