This utterly charming film set in World War II-era London contains a textbook example of screen chemistry. Rating: 3.5 stars out of 4.

Screen chemistry is an odd thing; often you only notice it when it isnt there. (See: far too many Hollywood romantic comedies.) But Their Finest, an utterly charming film set in World War II-era London, contains a textbook example. Gemma Arterton plays Catrin Cole, a young advertising copywriter hired by the British Ministry of Information to write womens dialogue for wartime propaganda feature films; Sam Claflin is Tom Buckley, a wry fellow screenwriter whos not sure that her presence is necessary. Catrins married, Toms not and so first they become co-workers (he grudgingly admits, eventually, that shes doing a good job), then friends. Watching them, you start noticing how he looks at her like shes a fascinating puzzle that hes trying to figure out, and how she blushes just a bit when hes around, and how effortlessly these two actors convey that they belong together.

Its one of many pleasures in Lone Scherfigs film, based on a 2009 novel by Lissa Evans and drenched in a sweet nostalgia that only very rarely tips into sentimentality. The plots mostly centered on the making of one movie, based on a true incident involving a pair of twin sisters who set out in their fathers shabby boat to help evacuate wounded soldiers at Dunkirk. Its a tale that, as the executives at the Ministry gleefully observe, has everything: Authenticity, optimism and a dog.

We watch the casting process (Bill Nighy, eyebrows perpetually raised, is a delight as a pompous veteran actor), the location shoot (note the 1940s version of CGI), and the way that the filmmakers and cast form an impromptu family. Along the way, were reminded of the new roles that women took on during that time, and how the shadow of war affected every day and every life, even as they soldiered on. And theres one scene, where Sam sits moodily smoking one evening, and Catrin appears behind him as if caught in a moonlit dream, and well, thats why we watch movies, isnt it?

Their Finest, with Gemma Arterton, Sam Claflin, Bill Nighy, Jack Huston, Helen McCrory, Jake Levy. Directed by Lone Scherfig, from a screenplay by Gaby Chiappe, based on the novel Their Finest Hour and a Half by Lissa Evans. 117 minutes. Rated R for some language and a scene of sexuality. Several theaters.

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'Their Finest' review: Wartime film sizzles with chemistry - The Seattle Times