The year is 1940. England has just suffered a massive defeat at the hands of Nazi Germany at Dunkirk with tens of thousands dead. There is a ray of hope. In the midst of the chaos, two sisters sail their small boat to Dunkirk to save as many soldiers as they can. They become heroes in the evacuation that saved hundreds of thousands of troops, giving hope to the defeated Allied troops.

Or at least, that’s how the British propaganda machine is selling it. Their Finest follows Catherine Cole (Gemma Arterton), born Catrin Pew, a comic writer hired by the British film department to write the slop (or women’s dialogue) in their feature films. They are in search of an uplifting story to rally the women and families on the homefront. Their tag line is authenticity and hope. And what is more hopeful than a true story of bravery?

The problem lies in finding a story that fits the desired profile. As Tom Buckley (Sam Claflin) tells Catrin: “Don’t confuse fact with truth and never let either get in the way of a good story.” The result is a look at the creation of stories and our fascination with those projected on the silver screen.

Their Finest is structured similarly. It’s a film full of substance disguised as light entertainment. It’s completely charming, full of quick quips and witty banter. For people who want to be transported into the past, Their Finest is a delightful diversion. But underneath this entertaining exterior, there is a substantial base. It’s an in-depth look at the importance of film as propaganda, unpacking the “based on a true story” films that are all more or less identical.

Everything is beautifully nuanced, from the importance placed on appealing to the female demographic and the emphasis on writing the slop, to the importance of Catrin’s/Catherine’s name. Arterton plays Catrin with a quiet ferocity. She manages to dominate the room and shrink into the scenery simultaneously. The script from Gaby Chiappe is sharp and on point, jumping from quick one-liners to in-depth exposition and back again, deftly walking the precarious tightrope between intellectual and popcorn entertainment. Lone Scherfig’s direction gives the whole thing a wistful air for the past and a hope for a brighter future. A future where “women’s stories” are just as important as the men’s.

Their Finest could be described as a perfect film. It’s not overt like the propaganda that is its focus. Instead, it subtly lays out its arguments and its story so that by the time you realise what Scherfig is doing, you are too enthralled to care. And that’s good propaganda.