‘Darkest Hour’ (B)

As she’s being prepped for her first day with

Winston Churchill (Gary Oldman), his new secretary (Lily James) is warned,

“He mumbles, so it’s almost impossible to catch everything.”

Mercifully, he’s not too difficult to understand.

But Oldman so disappears into the character, with the help of untold pounds of prosthetics and padding, it’s as though director Joe Wright (“Atonement”) discovered a brilliant, portly, 60-something actor just walking about the streets of London.

Focusing on Churchill’s first few weeks as prime minister, “Darkest Hour” opens on May 9, 1940, as Hitler stands poised to conquer Europe, the entire British Army is stranded in France and the British Parliament has lost faith in its leader, Neville Chamberlain (Ronald Pickup).

The 65-year-old cigarchomping, booze-swilling Churchill, who holds court in bed and dictates speeches while splashing around in the bath, replaces Chamberlain the next day.

King George VI (Ben Mendelsohn) wants nothing to do with him. Chamberlain immediately begins plotting his ouster. He’s constantly being told to seek a peace treaty with Hitler. And there’s the neverending problem of getting those 300,000 troops home from France.

If you’ve seen “Dunkirk,” that movie makes for a pretty big spoiler, but the two films actually complement each other quite nicely. And “Darkest Hour” demonstrates how, considering that everything and most everyone were working against Churchill, it’s fairly extraordinary that there’s still an England. scientists have developed a method of shrinking people to approximately 0.0364 percent of their current mass and volume.

Many of those who undergo the cellular reduction do it so they’ll consume fewer natural resources and extend the life of the planet. Paul and Audrey Safranek (Matt Damon, Kristen Wiig) sign up once they learn their $152,000 in equity has the equivalent value of $12.5 million inside New Mexico’s Leisureland Estates, which boasts dollhousesized Mcmansions, three Cheesecake Factories and a teeny, tiny Tony Roma’s.

“Downsizing” hails from director and cowriter Alexander Payne (“Sideways”), but the idea of a 5-inch Matt Damon can’t help but seem like a practical joke concocted by his TV nemesis, Jimmy Kimmel.

Once inside Leisureland, nothing is as Paul imagined. Then, after reluctantly attending a party thrown by his Serbian playboy neighbor (Christoph Waltz), Paul has a chance encounter with Ngoc Lan Tran (Hong Chau), a Vietnamese dissident who was downsized against her will and gained international fame as the only survivor among a number of itty-bitty immigrants who stowed away inside the packaging of a TV bound for America.

She now works as a cleaning lady.

Chau is phenomenal as the hilariously bossy ball of wonder who takes over Paul’s life. The