“So, our area is very much surrounded by the military. They are my

neighbors, they go to my church, they send their kids to local schools. I had this really great neighbor, he was a naval chaplain, but he primarily served with the Marines.

“He went to Afghanistan and because he was a chaplain, he was the one who rushed to these kids’ side when they were dying.

Efron's character walks to Louisiana in search of a girl in a photo

“He never carried a rifle, but over and over again, he literally held them as they died. He came back a second time and then went a third time. As he would tell me about what it had been like, his hands wouldn’t stop shaking.

As a community volunteer, said Sparks, “I coach track and field at a local high school and a number of my former athletes are in Iraq and Afghanistan now. When they come back, they are different.

“I have kids that I’ve coached who’ve been there and back and going again, they’re 20. I mean they are just kids — not 38-year-old veterans. They are kids. They told me how your squad goes on patrol with the squad you’re replacing.  The first week, you walk with them out front. The next week, you walk up front and the old patrol is in the back.

“The following week, old patrol is gone. You’ve got three weeks to figure it all out. One of the kids that I coached got into a firefight in Afghanistan. I think he was 19 and was there with his best friend. They got pinned down and his friend took a bullet through the head and died in his arms.

“This former high school track runner comes back and doesn’t understand how everybody just expects him to just go to the grocery store and fill up his tank at the self-service pump like anybody else.

Efron with actress Taylor Schilling, who plays the girl in the snapshot

“He’s seen his friends die. He has killed people in anger. The differences manifest themselves in a lot of different ways. You have some who might toy with suicide or drink too much or they’re unemployed. Most do just fine – they adjust and resume their lives. But some of them have trouble readjusting to society.

“Logan is one of them. He is a guy who says, ‘I lost all my friends,’” said Sparks, “and people don’t understand that he watched them die.

“His solution is to walk across the country and find the girl in the photo. This was the equivalent of my friend’s hands shaking and he didn’t know what to do to stop it.”

And so, Zac Efron as Logan just sets off walking with his dog – in search of a girl in a photo.

And what he lives is a Nicholas Sparks love story.

In it, he grows up – as an actor as well as a Marine.

The Lucky One opens in theaters nationwide April 20.