A professor, played by Viggo Mortensen, centre, is seduced by Germany's national pride during the early 1930s in the film Good. (TIFF)

Viggo Mortensen sees his latest film Good as a parable about good people who do nothing.

In the film, directed by Vicente Amorim, he plays John Halder, a university professor and intellectual in Germany in the 1930s.

As Halder makes decisions that lead him into moral decay — including an affair with a beautiful young student — his country is also inching down a disastrous track.

"It's not about Germans or Germany … It shows you how little compromises or little decisions can take a person or a nation down the wrong track," Mortensen said in Toronto, where the film screened at the Toronto International Film Festival.

Halder is so preoccupied with his mother, his children and his life, and blinded by nationalism, that he fails to notice the ominous political winds.

"In the beginning when you see Halder, he's almost like a rebellious intellectual … If you saw him in those early scenes and saw him in uniform later you'd say 'no way that's the same person' ... [this movie makes you] see the journey," he told CBC cultural affairs show Q.

It's only when a Jewish friend is sent to a concentration camp that Halder loses his complacency

"You could have a blurb that says: 'Doing nothing is the most dangerous thing you can do,'" Mortensen said.

Mortensen, 49, has played characters faced with complex moral dilemmas in films such as Eastern Promises and A History of Violence.

Good is based on a 1981 play by British writer C.P. Taylor. Mortensen recalls seeing the original production of Good in New York at the beginning of his career, with British actor Alan Howard playing John Halder.

"It was memorable, it was amazing, the people who've seen that production or saw early productions of that play have interesting stories— it has this almost legendary status," he said.

When he was sent the script to Good, he immediately remembered the moral landscape charted by the play, which treats themes of nationalism and individual responsibility.

"It's the decisions that individuals make from moment to moment added to all the other decisions moment to moment that other people make in a geographical area … and that's what we say is a nation," Mortensen said.

Good has not yet set a date for commercial release.