The Third Reich clashes with the Second in David Leveaux’s World War II-set drama, in which the single best moment is a dinner scene in which the exiled Kaiser Wilhelm II (Christopher Plummer) faces off against SS Heinrich Himmler (Eddie Marsan), where the ebullient gentility of the erstwhile emperor and the soft-spoken malignity of the Reichsfuehrer are skillfully, and understatedly, contrasted. Unhappily, most of “The Exception” focuses on an insipid romance between Captain Stefan Brandt (Jai Courtney), the newly-appointed head of Wilhelm’s German security detail, and Mieke de Jong (Lily James), a maid in the Kaiser’s household who, as it turns out, is not only Jewish but a British spy. In concentrating on them, the movie aspires to achieve the feel of a modern-day “Casablanca.” Instead it comes across like a younger cousin of “Allied.”

The premise of the script adapted by Simon Burke from Alan Judd’s novel “The Kaiser’s Last Kiss” is that in 1940, just after the Blitzkrieg has succeeded in seizing control of Holland and Belgium, Hitler decides to open a channel of communication with Wilhelm, the deposed German emperor who has been living on an estate outside the town of Doorn in the Netherlands with his second wife Hermine (Janet McTeer), whom he had married in 1922. The couple and Wilhelm’s loyal adjutant Sigurd von Ilsemann (Ben Daniels) are hopeful that the Nazi regime, obsessed with the idea of identifying with the greatness of Germany’s past, might be interested in returning Wilhelm to the throne as a symbol of German unity.

The little suspense that the picture generates from the political perspective derives from whether Mieke’s assignment is to assassinate Wilhelm—after all, she does keep a gun hidden in her room—despite the affection she obviously develops for the old duffer, whose main occupations—apart from looking over maps and making cracks about Hitler’s clumsy strategy—appear to be chopping wood with his one good arm and feeding the ducks in his estate’s little lake. There’s also some tension intended in whether the occupiers will be able to trace the source of the radio transmissions between Doorn and England that keep Mieke in contact with her handlers. But through the village priest is eventually caught and tortured, the suspense is undermined by the characterization of the local SS commandant, Dietrich (Mark Dexter), as such a clueless buffoon that he might have been recruited from the set of “Hogan’s Heroes.”

Dietrich, of course, is designed as a complete contrast to Brandt, the exception of the title—the “good German” who defies Nazi brutality. It’s a cliché films have seized on ever since “The Desert Fox” and “The Young Lions,” and it has grown mustier and mustier over time. The film isn’t helped by Courtney’s blandly strutting performance as the conflicted captain. James is no more impressive, especially since she begins their romance by simply complying when the German, at their very first meeting, tells her to take off her clothes. We’re meant to believe that their relationship is a love for the ages, but it never seems authentic, just a movie convention.

There is compensation, however, in some of the other acting. McTeer is superb as Wilhelm’s wife, quickly intervening to explain away her husband’s sometimes embarrassing slips while seeking to ensure that the financial support they’ve come to depend on isn’t reduced, and Marsan delivers a chillingly restrained portrait of pure evil in his few scenes as Himmler. Daniels is fine as a man of absolute loyalty, too.

But the film’s true saving grace is Plummer, who, if you’ll pardon the pun, recognizes a plum role when he sees it and savors every bite, bringing a degree of energy to the proceedings that Leveaux’s pedestrian direction otherwise dampens. The script doesn’t ignore the exiled ruler’s darker traits—his clear anti-Semitism, for example—but it underplays them in portraying him not only as essentially a charmingly old world figure who deplores the Nazis’ crudeness, but as an avuncular fellow who understands—and assists—the young people’s romance when push comes to shove. If the record is anything to judge by, this amount to as radical act of historical revisionism as one finds in the recent “Churchill”—the real-life Wilhelm was an extremely strange, perhaps psychologically damaged man. But whatever the facts might be, Plummer seizes on the screenplay’s view of him as essentially a genial old coot and milks it for all it’s worth.

Burke’s script shows a propensity to sink to lower levels when it seems to assume audience ignorance in off-the-cuff ways. Not once but twice characters feel compel to tell us who Himmler was when his name is mentioned. When Brandt is informed by Dietrich that “the head of the S.S.” is coming to dinner at Wilhelm’s, for example, the surprised captain blurts out, “Himmler?” to which Dietrich replies, “You catch on quick.” Indeed. The same device is employed a second time between two other characters, adding to the conclusion that the filmmakers don’t consider potential viewers to be very bright.

They have, however, done expert work from the technical perspective. Hubert Pouille’s production design and Daniela Ciancio’s costumes capture the period, and cinematographer Roman Osin uses the Flemish locations nicely. In short, “The Exception” is historically convincing in the visual details but completely bogus in terms of narrative, in particular the pallid central romance. Even Plummer’s canny old man routine isn’t enough to make up for that.