As far back as last fall, there were those in the New York theater industry whispering that the new musical “Come From Away” might turn into the 2016-17 season’s sleeper success story. But it sure didn’t seem likely: Here was a modestly-scaled musical from a pair of unknown writers with no stars in its small ensemble cast, tackling the serious, sensitive subject of the Sept. 11 terrorist attacks and their aftermath.

But despite long odds, “Come From Away” snuck onto the scene to become a burgeoning hit, both with New York critics and with Broadway audiences, who are fueling million-dollar-plus weeks at the Schoenfeld Theater. The show made news in March when Canadian Prime Minister Justin Trudeau and Ivanka Trump took in a performance together, and then again in May when “Come From Away” scored seven Tony nominations including one for the top award for new musical. It’s since shaped up into the dark horse contender that just might snatch the crown away from frontrunner “Dear Evan Hansen.”

What looks like sudden success for the $12 million musical, however, actually came after producers and creatives plotted a two-year, five-stop road to Broadway that helped fine-tune the show, shape marketing and build audiences. “We knew we had to build up an audience base,” said Sue Frost, one of the partners in Junkyard Dog Productions, which is lead producer on the show. “It’s a title nobody understands, it’s an ensemble cast with no stars, and everybody’s gonna call it the 9/11 musical.”

“Those were the three strikes we had going in,” agreed fellow Junkyard Dog principal Randy Adams.

But among the things the show had going for it was its potentially tricky, undeniably powerful, true story. Set in the tiny Newfoundland town of Gander and written by Irene Sankoff and David Hein — whose sole previous credit was Toronto Fringe hit “My Mother’s Lesbian Jewish Wiccan Wedding” — “Come From Away” chronicles the real-life tale of the town’s big-hearted efforts to host the thousands of diverse air travelers rerouted to Gander in the immediate wake of 9/11.

Although the subject matter’s direct link to the events of 9/11 made the creators’ job a delicate one, it also made the show a headturning human interest story. As it made its way around North America and then to Broadway, “Come From Away” sparked a flurry of profile-lifting news coverage of the musical’s links to real life — including, for instance, a New York Times story about Tony-nominated actress Jenn Colella and the pioneering pilot she portrays in the show. In addition, the musical’s theme of welcoming diversity in a time of division also imbues the title with a strongly contemporary political resonance — which made the headline-grabbing Trudeau-Trump visit feel especially symbolic.

Another press opp came between the musical’s stop in D.C. and its run in Toronto, when the cast and creative team took “Come From Away” home to Gander, performing the show — in the hockey rink, the largest venue available — for the townspeople who inspired it.

Meanwhile, producers and creatives made good use of the circuitous pre-Broadway route that saw the production play the La Jolla Playhouse and Seattle Rep in 2015 before 2016 stops at Washington, D.C.’s Ford’s Theater and Toronto’s Royal Alexandra Theater (with the detour to Gander between D.C. and Toronto). For one thing, the cross-country exposure endowed the show with a broad base of supporters before it ever set foot on Broadway.

“By the time we’d opened in New York, 250,000 people had seen this show,” Frost said.

Those four pre-Broadway productions also gave creators and cast members — most of whom have been with the show since La Jolla — the opportunity to finely calibrate the production’s depiction of a time that still looms large in many people’s memories. “I have never worked on a show where the audience has brought as much emotion into the theater with them,” said Ashley, who’s nominated for a Tony for his work. “Trying to find the balance of the light and the dark was an ongoing question, always.”

The production’s marketing message was also refined during the long run-up to Broadway, with a visit to the National September 11 Memorial and Museum in New York helping to solidify the idea that “Come From Away” isn’t about 9/11 — it’s about 9/12, and everything good and bad that came in the wake of terrible events.

On Broadway, audiences, augmented by out-of-town buzz, began to snowball, and box office really kicked into gear following the strong reviews the show earned after its March 12 opening. Among the crowds turning out are the array of specific communities touched by the story, including Canadians (particularly Newfoundlanders), 9/11 survivors and their families, and the airline community.

The show’s producers — who have opted for a less aggressive advertising strategy during Tony season than some of the musical’s competition — point to stellar word-of-mouth as the core of the production’s success. That enthusiasm has spread to Tony voters, too, but whether it’s enough for a top trophy win will be seen in the final moments of the awards ceremony June 11.