It was a single photograph that started Oscar- winning filmmaker Steve McQueen on the journey to make “Blitz.” As a Londoner, the German bombing raids on the city during World War II are never all that far from his mind. Reminders of it are everywhere.

But the spark of inspiration came from an image of a small boy on a train platform with a large suitcase. Stories inspired by the evacuation are not rare, but this child was Black. Who was he, McQueen wondered, and what was his story?

The film — now in theaters and streaming Nov. 22 on Apple TV+ — tells the tale of George, a 9-year-old biracial child in East London whose life with his mother, Rita (Saoirse Ronan), and grandfather is upended by the war. Like many children at the time, he’s put on a train to the countryside for his safety. But he hops off and starts a long, dangerous journey back to his mom, encountering all sorts of people and situations that paint a revelatory and emotional picture of that moment.

Searching for George and finding a star

When McQueen finished the screenplay, he thought to himself: “Not bad.”

Then he started to worry: Does George exist? Is there a person out there who can play this role?

Through an open casting call they found Elliott Heffernan, a 9-year-old living outside London whose only experience was a school play. He was the genie in “Aladdin.”

“There was a stillness about him, a real silent-movie-star quality,” McQueen said. “You wanted to know what he was thinking, and you leant in. That’s a movie-star quality: A presence in his absence.”

Elliott is now 11. When he was cast, he’d not yet heard about the evacuation and imagined that a film set would be made up of “about 100 people.”

But he soon found his footing, cycling in and out of the little vignettes along the way of George’s odyssey with stunts, slaps and all.

Elliott, for his part, preferred the days with stunts. “It’s just more exciting,” he said.

As his on-screen mother and co-star, Ronan, who remembers well the strange experience of being a child on a movie set, took him under her wing. Not only is he getting raves for his performance, but Elliott has also already booked another film (although he can’t talk about that yet). Another bonus: He has fully impressed his teachers with his WWII knowledge.

But can she sing?

Ronan told her agent she wanted to take a break after “The Outrun,” with one caveat: Steve McQueen. “He was like, ‘well, on that,’ ” Ronan said with a laugh.

“I was really excited by the idea that the love story that was going to exist in this kind of wartime epic would be a child and his mother. It was a story set during the Second World War that was going to stay on the ground. It was going to focus on the communities left at home and the ongoing war that they were facing every day that they stepped outside their front door.”

But McQueen needed a singer, and Ronan was an unknown quantity. They enlisted a vocal coach to visit her on a set where she was filming in Australia.

“I’ll never forget, I got a call saying ‘Steve, she can not only sing, but it’s only going to get better,’ ” McQueen said. “I was very happy to call her back and say ‘You got it.’ ”

Ronan and Elliott would get to sing alongside Paul Weller, the English rock star of the Jam and Style Council, in his first acting role as George’s kind grandfather. Rita also gets a solo showstopper in the original song “Winter Coat,” written by Nicholas Britell and Taura Stinson and inspired by McQueen’s late father. She performs it during a live radio broadcast at the munitions factory where she works.

Using the conventional to show the unconventional

Some critics have called “Blitz” McQueen’s most conventional, or traditional, movie. This, he thinks, is missing the point.

“There’s classical tropes, there’s classical situation. For lack of a better word, it’s a Brothers Grimm fairy tale to some extent,” he said. “But what it is showing is totally revolutionary. It’s using the conventional to show the unconventional.”

This means taking audiences inside places they’ve never been: the tube station at Stepney Green where East London residents took shelter from the bombs; the munitions factory; the ritzy Café de Paris, where another class of Londoners enjoy oysters and champagne to the music from the house band playing “Oh Johnny” as the bombs fall; and the tube shelter where a flood killed 66 people.

“Blitz” also introduces audiences to people they’ve likely not heard of: Mickey Davies (played by Leigh Gill), a man known as “Mickey the Midget” who turned the Spitalfields Fruit and Wool Exchange into a shelter; and Ife (Benjamin Clémentine), a Nigerian air-raid warden who bonds with George and was inspired by a real person.

Everything in “Blitz” was drawn from historical fact. And most of it is seen through the eyes of a Black child. George, McQueen said, is not Oliver Twist.

“It’s like comparing me to Prince Harry,” McQueen said. “Like, really? But that’s to do with something else. That’s whatever that is. But the reality is, I’m interested in images and stories that haven’t been told before.”

Going for the heart

McQueen doesn’t lose sleep over the big set pieces: the flood, the fire and the Café de Paris destruction. But he does worry about the emotion of it.

“Cinema is about the heart,” he said. “What gave me sleepless nights was creating the love and that the people felt it and it was palpable in the family. … This movie, at the end of the day, is about love. L-O-V-E.”

Film festival audiences are responding as he hoped. Now everyone else is getting the chance to go on this journey with George.

“It’s been getting a very visceral response from people,” McQueen said. “I think in London and New York, there wasn’t a dry eye in the house. It’s what cinema can do, and that’s what I wanted. It’s as much about the audience: You can see yourself through a child’s eyes.”