Their Finest

In London in 1940, Catrin Cole is hired by the Ministry of Information to help write scripts for propaganda films. Her male colleagues need her to craft realistic dialogue for female characters, but they pay her less than a man's wage and refuse to credit her. Her husband Ellis – a war artist, Spanish Civil War veteran, and volunteer air raid warden – seems indifferent to her achievement in getting the job.
Catrin is sent to interview two twins named Lily and Rose Starling, who supposedly participated in the Dunkirk evacuation. They tell her that they never reached Dunkirk because their boat broke down, although they did take on soldiers from an over-crowded tug returning the other way, causing newspaper reporters to believe they had come from the combat zone. After Ellis tells her he cannot afford to keep them living in London, Catrin lies to the Ministry and claims that the Starlings did reach Dunkirk. Her boss Roger Swain is impressed and greenlights the film, with Catrin seconded to the production company with extra pay.
While German bombs fall on London night after night, a viable script quickly takes shape, despite frequent arguments between the writers about factual accuracy versus artistic license and the needs of wartime propaganda. Catrin particularly clashes with Tom Buckley, who repeatedly belittles her contributions and tries to sideline the female characters in favour of male heroes. She is reassured by Phyl Moore, one of the few other women on the film. A fading actor named Ambrose Hilliard initially refuses to be in the film, until his agent dies in an air raid and is replaced by the agent's sister Sophie. Catrin is nearly caught in a bomb blast, and vomits after seeing a dead body.
Swain discovers that the Starlings did not reach Dunkirk, but is persuaded by the writers that the new story expresses a greater truth. Buckley covers for Catrin by claiming it was the twins who lied. The Secretary of State for War adopts the film as a way to build public support for Britain in the United States, ordering the writers to create a role for a real-life American flying ace. Meanwhile, Ellis is commissioned to document bomb damage far outside London, and is hurt when Catrin refuses to drop her job and go with him. She promises to attend his subsequent exhibition in London.
Filming begins in Devon. The American pilot turns out to be an abysmal actor, and the production is only saved by Catrin's interventions. Catrin and Buckley grow closer, as he begins to respect her work and she warms to his dark sense of humour. Discussing the difference between reality and fiction, Buckley recalls how the First World War broke his father's spirit, and argues that stories help people by giving them a sense of structure and closure.
The extra work means Catrin misses the opening of Ellis's exhibition and must rush back to London to catch its final day. Before leaving, she reveals to Phyl that she and Ellis are not married but pretend to be for propriety. In London, she walks in on Ellis having sex with another woman and storms out, snarkily rejecting his pleas and returning to Devon.
Buckley has found out about Catrin's non-marriage, and on a moonlit night he denounces Ellis and proposes to her. She refuses, prompting an argument. Back in London, the film's American distributors demand an ending with more "oomph", but Buckley is in a romantic funk and fails to write anything satisfactory. Catrin spends all night writing the ending, then types out a mock script returning to the night of their quarrel and providing a meaningful resolution that they could not find in the moment. In the morning, she finds her home has been destroyed by a bomb.
At the studio, some staff are missing due to air raids. Buckley and Catrin talk and reconcile. As he walks away, a lighting rig collapses on him and crushes him to death. Catrin is devastated, but manages to resolve one final plot hole – all the male actors who could shoot a missing scene are injured or unavailable, so one of the (fictional) Starling twins finally gets to save the day – before going into seclusion. Hilliard is also injured, and is visited in hospital by his new agent Sophie with offers of work and an offer to let him recuperate in her home.
The film, named The Nancy Starling after the Starling twins' real-life boat, is a hit, though Catrin misses the premiere. The real Starlings tell her the film has inspired them to run away from their bully of a father and join the ATS. Afterwards, Hilliard visits Catrin to enlist her help with a new film about air raid wardens, but she says she cannot write any more and breaks down crying. He comforts her, saying that they have been allowed to contribute their talent because young men are dying on the front lines. On his advice, she goes to the cinema to see The Nancy Starling and is moved both by the film and the audience's reactions. She returns to the scriptwriters' office to work on the new picture.