At the beginning of May 1940, Adolph Hitler was poised to invade Belgium, Holland, and France. Less than three weeks later, German Panzer and Luftwaffe divisions were within striking distance of wiping out over 300,000 British troops at Dunkirk (for a graphic look that battle, see this year’s “Dunkirk” from director Christopher Nolan) and crossing the English Channel into Britain.

At the same time, the British Parliament had taken a vote of no confidence in Prime Minister Neville Chamberlain (Ronald Pickup) due to his failed attempts at “appeasing” Hitler’s quest for world domination. When Chamberlain’s party met to choose a new prime minister, their first choice was Viscount Halifax (Stephen Dillane), who had been Chamberlain’s liaison to Hitler. But, Halifax declined, leaving Lord Winston Churchill (Gary Oldman) as the obvious, but unpopular, successor.

In “Darkest Hour,” director Joe Wright, working from a script by Anthony McCarten (“The Theory of Everything”), examines this troubled time through the lens of Churchill’s career. “The British Bulldog” demonstrates how he earned that nickname as he is introduced dictating messages to his new secretary, Miss Layton (Lily James). Churchill’s impatience almost scares Layton away. However, intervention by Churchill’s wise and devoted wife (Kristin Scott Thomas), plus a telegram from King George (Ben Mendelsohn), mend the relationship at a time when the new prime minister will need all the support he can muster.

While “Darkest Hour” focuses on the historic events of May 1940, it isn’t solely an historic drama. It also provides a psychological portrait of Churchill. Director Wright uses various techniques to extract and express Churchill’s internal struggles. The sounds of Hitler’s rants are background noise when Churchill contemplates his enemy’s character, leading to a verdict of “savage.” Churchill’s military advisors run footage of Nazi troops and express the belief that a Nazi invasion of England is inevitable. Churchill’s refusal to accept such an invasion is revealed by the rewinding of them military footage, visually reversing the potential victories of the Nazi forces.

The prime minister’s initially rocky relationship with King George also appears in “Darkest Hour,” as do both men’s struggles with speech impediments. Churchill’s perceived shortcomings are expressed by various characters including the king, Chamberlain, Halifax, and various members of Parliament. Despite those critiques, Oldman’s Churchill still comes across as admirable. He knows his own vulnerabilities and isn’t afraid to reveal them in conversations with both the public and the king. Despite being well-educated, Churchill admits his aristocratic upbringing means he has no real experience of the lives of everyday Britons. Yet, he is not above reaching out to those people and is willing to share a good laugh with them, even when it is at his own expense.

“Darkest Hour’s” storyline follows the events of May 1940, utilizing a graphic calendar to track the dates for the audience. The film’s excellent cast features familiar faces from TV’s “The Crown,” “Downton Abbey,” and “Game of Thrones.” Dillane as Halifax is a perfect passive aggressive foe for Oldman’s Churchill. Halifax doesn’t want the responsibilities of being prime minister, yet he also has no love for Churchill since the latter opposed moves toward appeasement. Pickups Chamberlain displays both conflict and political one-upmanship as he maneuvers in the shadows. The musical score by Dario Marianelli heightens the sense of tension between Churchill, Chamberlain, and Halifax.

The political reluctance in both Britain and America to become involved in yet another world war is well-illustrated. Halifax and Chamberlain are tireless in their calls for appeasement and/or negotiated settlement with Hitler. When Churchill calls President Roosevelt in hopes of procuring military supplies from his friend across the Atlantic, Oldman’s body language conveys Churchill’s discouragement as the president says his hands are tied by the American Neutrality Act.

As Lady Churchill, Kristen Scott Thomas’ performance provides a glimpse into the strength and wisdom of the prime minister’s wife. Glances between Churchill and some of his children hint at inter-generational tensions. But, Thomas’ Lady Churchill remains supportive, even when frustrated by her husband’s behavior.

The era’s historic tensions play out against detailed sets designed by Sarah Greenwood and decorated by Katie Spencer. The locales range from the opulence of Buckingham Palace to the spartan accommodations of the military bunker used by Churchill and his War Cabinet. Churchill’s historic speeches to the British public via the BBC and to Parliament are included. Greenwood’s set for the floor of Parliament, combined with Bruno Delbonnel’s cinematography, seem to shrink that space, making the political debates border on claustrophobia.

Ultimately, two scenes near the end of the “Darkest Hour” truly capture the heart of the film. In the first, King George and Churchill finally confer with one another. And, in the second, the prime minister reaches out to the people of London. Via these two interactions, Churchill gains the direction and confidence necessary to see Britain through to victory against Nazi fascism. And, the audience is reminded of the value of honest communication.