When Baltimore Opera learned that the lead soprano in its production of Verdi's Rigoletto had canceled less than two weeks before the start of the run, and that the replacement star could not fit tonight's opening performance into her schedule, it was time for a burst of the-show-must-go-on action.

Enter Nicole Biondo.

This Baltimore native was already preparing to sing two subsequent performances in the opera as Gilda - her debut in the role and, more remarkably, her first attempt at any soprano role, let alone a starring one. Every previous time Baltimore Opera audiences have heard her during the past eight years, Biondo was singing secondary mezzo-soprano parts, as in last season's Faust.

"When she auditioned for me and sang the whole part [of Gilda], I thought we should give her a chance," says Baltimore Opera general director Michael Harrison. "And when Youngok couldn't do the opening night, I felt Nicole should get that chance, too. She's been working extraordinarily hard on it."

For Biondo, it's the fulfillment of a long-standing goal.

"In my heart, I wanted to be a soprano," she says. "My teachers knew I had the potential. And one of my colleagues told me he could tell I was going to change to soprano. He joked that when he heard me vocalizing backstage, I would go up to a 'K.' "

Even without hitting that imaginary note, Biondo felt confident that her natural range was really above the mezzo level. She began working on the shift about two years ago and soon felt confident enough to seek the audition for Gilda.

"The wonderful thing about Mr. Harrison is that he is very open to young singers," she says. "He was willing to give me quite a lot of work with the company as a mezzo-soprano. It gave me wonderful stage experience. I learned how to fence as Siebel in Faust and Stefano in Romeo et Juliette, and to play castanets as Mercedes in Carmen.

"But the greatest thing was working onstage with world-class singers - people like James Morris, Ruth Ann Swenson and Ghena Dimitrova. Nothing can teach you like that."

Biondo does not take her vocal climb lightly.

"These soprano roles require an amazing amount of commitment," she says, "along with the greatest range of vocal colors and the greatest range of expression you can find. You have to live the life of the character, and that has to come out in your voice. And you need a technique that will support you."

Biondo already has a short wish-list of soprano roles, starting with Manon in the Massenet opera of that name. But for now, she's focused on the emotionally fragile heroine of Rigoletto.

"Gilda's a great character, so innocent in her desire to make connections with people," Biondo says. "This is a perfect jumping-off spot for me, a great opportunity."

And a remarkable contrast to her first appearance in a Baltimore Opera production of Rigoletto back in 1994.

"I had the smallest role in the opera - the page," Biondo says. "Just three little lines. But, at the time, it was very exciting."