In late April, about 60 members of the Utah Symphony were on break during a rehearsal of Massenet’s opera “Thaïs” when the organization’s chief executive, Steve Brosvik, matter-of-factly told them that the county was considering demolishing Abravanel Hall, their world-renowned home, as part of a plan to revamp downtown Salt Lake City.

The musicians were in shock. How could this be? Abravanel Hall had housed the symphony for 45 years, built with gold-leafed bridges, crystal chandeliers and some of the finest acoustics in the country.

“We got really depressed,” said Lori Wike, the symphony’s principal bassoonist. “And then we started organizing.”

With that, Wike, a 47-year-old with no experience in local government, found herself entering the sharp-elbowed world of politics. She joined a small but vocal group of musicians in taking on mayors, lawmakers and the billionaire who owns the two major professional sports teams that play in downtown Salt Lake City.

The musicians dug through planning codes, attended council meetings and began a media campaign to publicize their cause. They enlisted the help of architects, opposition politicians and John Williams, the fabled composer of scores from classic films like “Jaws” and “Raiders of the Lost Ark.”

The task was formidable. City and county leaders were pushing ahead with an ambitious plan to remake up to 100 acres of downtown, largely at the behest of Ryan Smith, the owner of the N.B.A.’s Utah Jazz and his newly acquired N.H.L. team that will soon play in downtown Salt Lake City, along with two professional soccer franchises of which he’s a minority owner.