With a title that’s a shortened version of one of Winston Churchill’s most famous rhetorical flourishes (so memorable that he reused it on the spine of a volume in his massive history of World War II), you might expect “Their Finest” to be a typically stiff-upper-lip paean to British pluck during the Blitz. There is some of that spirit in the film, to be sure, but the surprise of Lone Scherfig’s adaptation of Lissa Evans’ novel is that it deftly balances humor and drama to fashion a picture of life under wartime stress that’s both richly funny and occasionally quite moving. But there’s more: the picture is both a heartfelt homage to, and a cheeky send-up of, the British filmmaking of the period, as well as a tale of women on the rise in society. A lot is going on in the “Their Finest,” and the fact that it juggles all of it so well is evidence of the skill of the director of “Italian for Beginners” and “An Education.”

The linchpin of the narrative is Catrin Cole (Gemma Arterton), a young Welsh secretary looking for a job in the summer of 1940, as German bombs are falling on London. Applying at the Ministry of Information’s film division, which makes short morale-boosting informational pieces to play before features in theatres, she’s not only hired but, since she has experience in copywriting, is assigned by her boss Roger Swain (Richard E. Grant) to the writers’ room alongside two male veterans of the trade, supercilious Tom Buckley (Sam Claflin) and mellow Raymond Parfitt (Paul Ritter), who work under the stern eye of office manager Phyl (Rachael Stirling). Catrin’s function will be to come up with what’s referred to dismissively as slop—the inane dialogue penned for female characters. Catrin is happy to land the job, despite the fact that—as Swain says matter-of-factly—she’ll naturally be making less than the men. But any salary will help her support her husband Ellis (Jack Huston), a painter injured during the Spanish civil war whose work is deemed too gloomy for War Office use.

She’s also buoyed by a special assignment—to interview twin sisters Rose and Lily Starling (Lily and Francesca Knight), who, according to news reports, took their father’s boat across the channel to Dunkirk as part of the effort to rescue soldiers stranded on the beach there. Their inspirational tale, it’s believed, might provide fodder for a movie, but reports of their exploit prove wildly exaggerated. Catrin pitches it nonetheless, and Buckley persuades Swain that fidelity to truth is less important than dramatic punch; besides, Tom’s former employer, producer Gabriel Baker (Henry Goodman), who’s anxious to use his skill to promote the war effort, embraces it wholeheartedly.

The actual making of the movie provides the backdrop for the remainder of “Their Finest,” with amusing details about thrashing out a script and the cheesy special effects. But the most important element involves casting—not so much of the supposed stars, who are photogenic but bland, but of the supporting players. One of them is Carl Lundbeck (Jake Lacy), a hunky American pilot who’s abruptly written into the plot—despite a singular lack of acting talent—at the urging of the Minister of War (a delicious cameo by Jeremy Irons), a frustrated actor who believes the appealing to the U.S. audience might induce the Yanks to abandon their neutrality and join the conflict.

That’s a plot thread that yields a few pleasant moments, but far more are provided by Ambrose Hilliard (Bill Nighy), a washed-up actor hired to play the heroic girls’ boozy old uncle. Painting a perfect portrait of a has-been unable to give up the pretense of being a matinee idol, Nighy embodies a man who believes the whole world should revolve around him, yet brings an underlying vulnerability to the character as well. In the process he steals every scene he’s in—including those with his agent Sammy Smith (Eddie Marsan) and Sammy’s hard-nosed sister Sophie (Helen McCrory), both excellent. One might be tempted to say that he does so effortlessly, but that wouldn’t be accurate, since one can see Nighy using every actor’s trick in the book to bring Hilliard to life; but the result approaches something like perfection. (A pity he and Irons don’t have a scene together.)

That’s not to say, however, that Arterton and Claflin are thrown completely into the shade. She brings warmth and strength to the part of a woman emerging from her shell, and he demolishes the image of the handsome stud from “The Hunger Games” with his turn as an undernourished, bespectacled cynic who gradually warms romantically to his office-mate, though he must struggle to overcome his outmoded sense of male superiority. As Catrin and Tom grow closer, of course, she must deal with Ellis, and this is the one aspect of the story that doesn’t come off; the relationship never feels convincing in the first place, but the means of resolving Catrin’s ambivalence has a rote quality. The filmmakers redeem themselves, however, with a twist that most viewers won’t see coming (and many will deplore). Like an earlier turn involving Sammy and Hilliard, however, it serves the salutary function of reminding audiences that all was not sweetness and light at a historical moment when things could change very quickly, and very brutally.

“Their Finest” makes do on a modest budget, and though that sometimes shows (the sequences of devastation as bombs rain down on the streets are small-scaled), overall the film looks fine, with nifty period detail provided by production designer Alice Normington and costumer Charlotte Walter and expert widescreen cinematography by Sebastian Blenkov; and while Rachel Portman’s score is occasionally overbearing, it fits with the film’s traditional visual style.

With a rich vein of comedy and romance in the midst of tragedy, an undercurrent of feminism and an overwhelming love of filmmaking itself, Scherfig’s movie touches many bases with remarkable dexterity, providing ample opportunity for a superb ensemble cast to shine along the way. The titular adjective is not out of place in this instance: this is one of the most sheerly enjoyable movies released thus far this year.