Al Pitrelli found a way to describe the Trans-Siberian Orchestra this summer when he was reading a biography of conductor Leonard Bernstein.

“He had a quote in there – ‘True art needs to be accessible, but never ordinary,’” Pitrelli said. “It kind of lit me up and I read that passage a bunch of times, over and over. I think that sums up Paul O’Neill and the Trans-Siberian Orchestra in one sentence.”

Guitarist Pitrelli has been with TSO since he was brought into the band by O’Neill in 1996 and now, after nearly 30 years of recording and touring, he knows precisely how the Christmas rock ensemble fits into Bernstein’s notion.

“It’s very, very accessible and it’s far from ordinary regarding the amount of different genres of music we perform – everything from Mozart and Beethoven symphonies through good old-fashioned American rock and roll, R&B, swing, choral pieces,” Pitrelli said. “Visually, it’s the biggest rock and roll band on the planet. And at the center of it is this incredibly sensitive, accessible, but not ordinary story that Paul O’Neill wrote.”

The story for this year’s tour by TSO is “The Ghosts of Christmas Eve,” a rock opera created by O’Neil that follows the journey of a runaway who breaks into an abandoned vaudeville theater on Dec. 24. It debuted on a 2001 DVD that combined the most popular songs from the TSO albums “Christmas Eve and Other Stories” and “The Christmas Attic,” It will be the centerpiece of this year’s show for a very good reason.

“We’ve noticed that people have kind of embraced this as part of the holiday tradition,’ said Pitrelli. “When we were kids, maybe it was ‘Charlie Brown’s Christmas’ or ‘Miracle on 34th St.’ or ‘It’s a Wonderful Life.’ ‘The Ghosts of Christmas Eve’ has become that for many, many people, ourselves included.

“We’ve got a bunch of people in the audience that have been coming to see us for 20-something years now and we affectionately refer to them as the repeat offenders because they want the familiarity. They keep coming back and they want to see that familiar portion of the show. We’re gonna give that to them again, in content, meaning the poetry, the songs, the characters that Paul O’Neill had written into the story. But everything (else) about the show is different.”

That “different” part of the show is infused with the spirit and philosophy of O’Neill, who died in 2017. O’Neill’s way of doing shows figures into TSO’s elaborate visual production, which changes every year, even if the story it is telling does not.

“Initially the decision on anything we do is ‘what Paul would think of this?” said drummer Jeff Plate. “This tour every year is different and it is better every year and, in some aspects, it is bigger every year. This was something that Paul just insisted on doing. He was never going to run out with the same show year after year.”

Those “what would Paul do” decisions aren’t just about the production. They include considering what new songs, if any, will be added to the second half of the show – a laser-lit presentation of TSO’s “greatest hits.”

“Certainly, the opening of the show is always different,” Pitrelli said. “We have a pretty deep catalog that Paul O’Neill has left us and we could draw from that. Then you know the back end of the show, you’ll have your five, six, seven songs that the folks in the audience really look forward to hearing. That leaves us like another half a dozen to say ‘Hey, you know we haven’t done that in a long time (or) … we’ve never done that.’ So it’s a fun process.”

That process begins in January when TSO management and producers start putting together the show that will go out for its two-month run in November.

And that show, from the music to the production, gets finely honed during a month of rehearsals in Council Bluffs, Iowa, where the two TSO troupes simultaneously rehearse, one at each end of the arena floor.

The bands are largely made up, year after year, of the same musicians, so the players are more than familiar with the music and how it is incorporated into the story.

Both troupes perform the same setlist. But, Plate said, the rehearsals reveal some differences in the musical approaches.

“We get to watch each other rehearse and it’s pretty cool because there are some things that the West group does and the East group does,” Pitrelli said. “That’s kind of cool, I think we might steal that idea’ and they do the same thing. There’s a lot of give and take in what we do, but it all starts in the same place.”

Putting together the show, rehearsing and touring for a couple of months is, Plate admitted, something of a grind. But it’s a grind that he, Pitrelli and those who return to TSO each year willingly undertake and it lets them live out their rock and roll dreams in an extraordinary fashion.

“We think about this stuff when we first start playing an instrument,” Plate said. “It’s that fantasy of being on stage and you’re playing in front of a sold-out arena. This tour is literally a sell-out from beginning to end. Everybody in that room is having a great time. They leave happy. There’s nobody that’s walking out of there thinking that ‘oh, that wasn’t all that.’ We put a lot of work into this.

“Paul struck on something that really connected with millions of people, and all of us on stage also,” he said. “That’s why you’ve got so many people that come back every year. When you connect like that, there’s nothing like it in the world. I’m gonna do this until I can’t.”

Trans-Siberian Orchestra brings its Christmas tour to Enterprise at 2:30 and 7:30 p.m. on Sunday, Dec. 17.