How does a performance of a 146-year-old comic opera qualify as a premiere? In the case of Gilbert and Sullivan’s Thespis, which the Durham Savoyards present this week, it’s because the score has been missing since the end of the 1800s.

This absence prompted composer Alan Riley Jones to begin writing his own version of the music in 1992. When he finished a score for piano and chorus for a staged reading in 2004, the Savoyards asked him to write an arrangement for a twenty-three-piece orchestrathe traditional number for Gilbert and Sullivan. After a trial performance last May, the company scheduled its premiere.

But what prompted the mysterious disappearance of Arthur Sullivan’s original score? Scandalat least in Victorian termscould be the answer.

Years before the pair became household names in England, Gilbert and Sullivan wrote Thespis for a London burlesque house. Billed as “An entirely original Grotesque Opera in Two Acts,” the production featured cross-gender casting, “brazen girls in tights and short skirts,” and broad humor that its creators would later denounce as “the kind of work they wished to avoid.” As a result, Thespis was never published or revived during their lifetimes. Conveniently enough, the score vanished thereafter.

The missing score “opened a door” for Jones, a longtime Gilbert and Sullivan aficionado. He tries to answer the question, “If I was handed this libretto in 1871, what would I have written in the style of the time?”

“Alan has the ear and tone of Sullivan,” says Savoyards president Bobby Cameron. Jones’s achievement inspired the company to stage Thespis as a second show this year, paired with Trial by Jury, Gilbert and Sullivan’s second comic opera. As such, they had to cut costs by staging it at East Chapel Hill High School’s theater, a surprisingly good venue for professional theater. The venue “lets us reach out to a new generation and get as many kids involved as we can,” Cameron says.

Thespis and Trial by Jury run Oct. 12 through 15; visit www.durhamsavoyards.org for times, tickets, and details.