When Hannah Arendt wrote of the banality of evil, she was referring to Adolf Eichmann but also describing the many small-time monsters who helped turn Nazi Germany into modern history's most enduring cautionary tale. They are incarnated in one John Halder, the fictional subject of Good, a subtle and quietly devastating film directed by Vicente Amorim from John Wrathall's delicately written adaptation of a play by C.P. Taylor.

Viggo Mortensen plays Halder, a middle-age professor beset by mundane problems: a crumbling marriage, an ailing mother, an undistinguished career. This last, his biggest weakness, will prove his undoing.

When Halder's obscure novel, about compassionate euthanasia, finds admirers in the Reich, the author is dazzled by the attention. Though he privately considers Hitler "a joke," he joins the Nazi party and soon finds himself rubbing elbows with the ruling elite. Slowly, Halder gains the confidence to divorce his wife (Anastasia Hille) and marry his pretty student, Anne (Jodie Whittaker), who loves him for his mind but also takes visible pleasure in his uniform.

Less pleased is Halder's Jewish friend Maurice (an excellent Jason Isaacs). The two men once bantered over pints, but now the personal is political. As the once-carefree Maurice devolves into a hunted animal, Isaacs imbues him with a combination of dignity and humiliation that's excruciating to watch.

Mortensen, best known for playing forces of nature (A History of Violence, Eastern Promises), is here all mild manners, spectacles and fawning body language. His Halder is a character who lacks character, and Mortensen subtly turns him into a pitiful, pitiable villain.

Throughout the film come brief moments of surreality that initially seem out of place. But in the end these weird shards come together to form a horrible looking glass. The reflection is not of Halder, who looks as normal as any of us, but of the hellish world he has helped create.

BOTTOM LINE: Powerful and chilling, this is the one film of the year that truly has something to say about the horrors of Nazi Germany.