Back in 2005, a high-security prison hosted an unforgettable play you’ve probably never heard of.

“Breakin’ the Mummy’s Code,” was created by Rehabilitation Through the Arts (RTA), a theater initiative for incarcerated men at New York’s Sing Sing Correctional Facility. This innovative musical, entirely written and performed by the inmates, featured a host of characters including gladiators, mummies, cowboys, and pirates in a fun, time-traveling adventure.

“Throughout our daily lives, we often lacked reasons to smile,” reflects Clarence “Divine Eye” Maclin, who played both Hamlet and Robin Hood in the show. “Coming together during those moments – and seeing everyone drop their defenses and be playful – those are the wonderful memories I cherish from putting this play together.”

The story behind this musical serves as the foundation for “Sing Sing” (hitting theaters nationwide on Friday), a compelling film featuring Colman Domingo as the real John “Divine G” Whitfield, who unjustly spent nearly 25 years in prison for a wrongful homicide conviction. The film chronicles Whitfield’s lengthy battle for clemency alongside his role in RTA.

Director and co-writer Greg Kwedar discovered the program through a Google search and came across a 2005 Esquire article by John H. Richardson titled “The Sing Sing Follies.” He was immediately captivated by the stark contrast between life in prison and the absurdity of “Mummy’s Code.”

“There was something about the playful nature of the production against the backdrop of a prison that represented the full spectrum of human experience,” Kwedar remarks. “It was vibrant; it carried such energy.”

‘Returning to that space stirred up much trauma’

Aside from a few professional actors, such as Paul Raci from “The Sound of Metal,” nearly all cast members were once incarcerated. Sean “Dino” Johnson, who spent 15 years at Sing Sing on a drug charge, was released in 2004. He was a founding member of RTA and eagerly seized the chance to act once more.

“I’ve been back home for 20 years now and had to take care of my responsibilities. I didn’t have the chance to pursue my passion for acting,” Johnson explains. “So when Greg presented this opportunity, I thought, ‘Now is the right time.’ ”

For Maclin, participating was a “no-brainer.” He was incarcerated for 17 years at Sing Sing for robbery, and after his release in 2012, he noted that RTA had been approached about several film and TV projects, but none felt “authentic.”

“Each time we spoke with someone, it felt like we were being used,” Maclin shares. “They just wanted to claim they assisted some unfortunate prisoners as a way to feel good about themselves. However, I didn’t sense that with Kwedar and his co-writer, Clint Bentley: “Their intentions were genuine and clear.”

Both Maclin and Whitfield were credited with the story in the film, helping to guarantee that

The dialogue captured during filming felt true to a prison environment. To ensure everyone’s well-being, Kwedar also brought in a therapist on set in case any of the actors experienced strong emotions. (The film was shot at the Downstate Correctional Facility, a location many of the cast members had previously encountered on their journeys to Sing Sing.)

“There was a lot of nervousness,” Maclin shares. “No one wants to willingly return to a prison where they were incarcerated, let alone wear that same prison uniform that marks you as state property. However, we realized the mission behind our work was more significant than any discomfort we might feel.”

For Johnson, returning to that environment was filled with painful memories: the walls, the odors, the still air. “It all came rushing back,” he recalls. “But I recognized a distinction: Years ago, I didn’t care how that state green uniform fit me. This time, I thought, ‘Let me find one that looks nice on me.’ (Laughs.) My perspective shifted to: ‘This is my choice. This isn’t something I’m forced to do. The doors are open, and I can leave anytime I want.’ ”

‘This means more than just a bucket list’

During the often emotional filming process, the cast and crew supported each other. (“They got used to seeing me cry,” Kwedar joked.) This camaraderie shines through as they promote their film, which has garnered critical praise and is being viewed by many Oscars experts as a strong contender for best picture. Maclin is also being predicted to receive a nomination for best supporting actor for his impressive performance in a debut role.

“When it comes to nominations and Oscars, I think Colman Domingo deserves it more,” Maclin graciously redirects the focus, but Kwedar jumps in to commend the entire cast.

“It feels strange to consider individual awards for what was such a collaborative endeavor,” notes the filmmaker. “That’s something we’ll need to reflect on in the future – we all prioritize celebrating each other’s achievements, while acknowledging the significant individual efforts put into this project across the board.”

Both Maclin and Johnson plan on continuing their acting careers and have a list of Hollywood icons they would love to work with, including Denzel Washington, Halle Berry, Tom Hanks, and Sandra Bullock. Their ideal project would be a remake of “The Dirty Dozen” featuring other RTA graduates.

After premiering “Sing Sing” at the Toronto Film Festival last fall, Maclin felt “blown away” by the audience’s response to their story. It was the first moment in his acting journey when he truly felt that a career in acting was within reach: “When they stood up, I realized this is much more than just a bucket list.”

Johnson felt uplifted by the positive reception as well. “For so many years, we’ve been conditioned to believe that the world isn’t interested in people with past incarcerations,” he reflects. Yet, he asserts, this film “is about people. We all face challenges. The resilience of the human spirit is remarkable, and we all have our breaking points.”