Nine out of 10 Rigolettos agree that for fast, fast, fast relief from terminal stage fright or temporary amnesia, nothing succeeds like a reassuring glance from the Metropolitan Opera's Joan Dornemann. "She's the underground diva of the Met," says baritone Sherrill Milnes, "In her face you can read her love of the music and the emotion of the moment." Yet the audience never sees Dornemann, who, as one of the company's four prompters, is fated to be an unsung heroine. "I hit all the high Cs," she says, "under my breath." Says tenor Placido Domingo: "Her smiling face makes me feel as if I have a secret friend onstage."

Dornemann, 42, might be better described as an aria-traffic controller. In her prompter's box, which has all the room and charm of an aging coffin, Dornemann watches a TV monitor focused on the conductor and with her left hand maintains his beat for the performers. With her right index finger she cues each singer and, just before each cue, softly speaks the words he or she is to sing. "She probably has the best timing in the house," says soprano Roberta Peters. "She has to be faster than the conductor and slower than the singer—at the same time." And when stars draw a blank, they look down to Joan for guidance. "Everybody has those moments," admits Peters, "and they are hairy."

When Dornemann isn't rescuing prima donnas in distress she's coaching them, as one of the Met's 13 assistant conductors, or working with young singers at home. "She'll teach anybody," quips her mother, Marilyn. "Even if they don't have any money." Or even if they do: One of her students was Linda Ronstadt, who was struggling, says Dornemann, with "the hard little cadenzas" in The Pirates of Penzance.

Marilyn says she knew from Joan's birth that "there was music in her soul." When the family moved from Boston to Long Island, where Joan's father works as a paperhanger, Marilyn paid for her daughter's piano lessons by breeding dogs. "She raised I don't know how many litters of cocker spaniels," recalls Joan, a self-described "short, fat and shy, shy, shy" little girl who had found a friend in classical music. "The piano keys would talk to you," she remembers.

After graduation from Hofstra University, she taught music and became an accompanist for opera students. Soon the romance of opera, nurtured by a romance with a young operatic basso, swept her off to Europe to learn Italian, French and Spanish. She also landed a job as a rehearsal pianist at Barcelona's renowned Gran Teatro del Liceo, where she was offered a chance to prompt. In 1974, after learning her craft—at a starting salary of $7 a day—and earning a respectable reputation, she received a call to audition for Met maestro James Levine. "If we can agree on a salary, we'd love to hire you," he said. "We'll agree, we'll agree!" Dornemann replied. "Tell me what it is and we'll agree!"

They did—at around $24,000—and nowadays Dornemann can't wait to climb back into her box. "When the curtain goes up I'm like Popeye after a can of spinach," she says. Over the years, her favorite moments have included the time a loose wire caused her chair to start smoking ("I couldn't leave—the opera wasn't over yet!") and the night a bat began flying around the stage and refused to be waved away ("You can't prompt a bat," Dornemann learned). But she's really happiest when the show goes smoothly and she can remain the phantom of the opera. Backstage at intermission, she often asks her friend, young conductor Paul Nadler, if he could hear her from the audience. "She's always relieved," he says, "when I tell her I couldn't hear her at all."