The film isn't yet made, but it will be based on the Erik Larson book of the same name and will star Tom Hanks.
The book, which the film is expected to follow quite closely, tells the story of a Professor William Dodd, who became US Ambassador to Germany in 1933 at the height of Hitler's Third Reich and brought his family to live in Berlin with him.
At first the Dodds, who greatly enjoyed life in Germany (especially his party-lovingdaughter), were relatively naive about Hitler's regime and what it would do; their own prejudices also played a part. Even when some of the atrocities, such as attacks on Jews, started, for some time Dodd remained unsure and was inclined to admire Hitler.
However, over time he became appalled by the Third Reich and increasingly tried to alert the US government to its true nature, with little success for a long time.