The greatest asset of the movie “One Life,” starring Anthony Hopkins, is the harrowing true story it’s based on.

You might not immediately recognize the name Sir Nicholas Winton, but you have probably seen the viral YouTube video of an old man learning on live TV that the studio audience around him is made up of people he rescued from the Nazis as children.  

If you haven’t, give it a watch. It’s profoundly moving.

Winton facilitated the risky and complex relocation of 669 mostly Jewish kids in Czechoslovakia to Britain during World War II — an operation known as the Kindertransport. When his herculean task was finished, he humbly returned to private life in England and rarely spoke of his heroic deeds again.

Decades later, on a 1988 episode of the BBC talk show “That’s Life,” Winton finally witnessed the enormous impact he made.

“One Life,” which premiered Saturday at the Toronto International Film Festival, expands on that touching clip and depicts the brave man’s time in Prague and his battle against British government bureaucracy to allow the imperiled children into the UK.

Hopkins plays the elderly Winton, who endures painful flashbacks to those terrifying days. An even-tempered Johnny Flynn takes on the role of the man’s younger self during the war, who is aided in the effort by his no-nonsense German expat mother Babi (Helena Bonham Carter) back home.

Director James Hawes’ film is an automatic tearjerker, no doubt about it. The story is too overwhelming not to have some effect on anyone who watches it — even the cranks. And as 85-year-old Hopkins has aged, his power as an actor has given way to deep vulnerability. We instantly and unwaveringly care about him.

Because Winton, who died in 2015, was known for his reserved demeanor, the role does not give Hopkins the opportunity to scorch the screen as he did in “The Father” all the way to a Best Actor Oscar win. Even his climatic emotional outpouring is rather reserved.

Nonetheless, his casting is ideal.

However a film is more than a plot line and a performance. When a movie wades into the vast pool of World War II and Holocaust titles, the viewer expects a splash. “One Life” is, at best, a spritz. It delivers a lot of what we’ve already seen before, but on a less-than-cinematic scale. 

Yet spending some time with Hopkins and exploring a speck of light in one of the world’s darkest chapters is just satisfying enough.