The job of understudy is one of the toughest in the business. It usually means you prepare like crazy for a moment that doesn't happen, or happens so seldom that you can't create something as rich, connected and involved as you or you fellow actors would like.

By the time Robert Goulet steps into the role of Georges on April 15, Hillner will have played the role in 32 performances at the Marquis Theatre. The actor's first brushes with Georges came because Daniel Davis took ill. Hillner's been singing Jerry Herman's "Look Over There," "With You on My Arm" and "Song on the Sand" in recent weeks because Davis and the producers had a parting of the ways.

Hillner, 52, is a Broadway veteran whose credits include They're Playing Our Song, Woman of the Year, Footloose, Big and more, as well as playing suitor Sam for a year in the pop musical Mamma Mia! at the Winter Garden. But he never played a leading man in a big traditional Broadway musical.

"As far as a lead on Broadway, to get this opportunity is really amazing," Hillner told Playbill.com. "Mamma Mia! is about three dads and three women and you're not standing out, necessarily."

For the consistently-employed Hillner, La Cage was a gig that included covering three roles and playing ensemble parts. It wasn't a lead or a feature, but "it's all work, why not?" Hillner said when he accepted the job. A friend told him at the time, "You never know what's gonna happen when you take a job." What happened was a surprise jump-in performance by Hillner in the first weeks of the run of La Cage in November 2004.

The secret that few theatregoers know is that understudies, with few exceptions, aren't rehearsed until after the opening night.

"A week and a half into previews, we had had no rehearsal," Hillner said. "It was the night after Thanksgiving — we had that funky weekend schedule with two on Friday and two on Saturday — and Daniel Davis was having vocal trouble. He had vocal trouble in the second show Friday night. I was listening to him in the monitors and I hoped he made it to intermission. I went upstairs, I got my contacts on, and I came back down. In the reprise, he stopped the orchestra and said, 'I can't go on. I'm sorry ladies and gentlemen, I have a virus. Give the understudy 10 minutes and he'll be on.'"

Hillner was "shot out of a cannon." He went to wardrobe and they costumed him, librettist Harvey Fierstein offered to vamp in front of the audience while Hillner learned the dance for "With You on My Arm."

Hillner explained, "Harvey goes out in front of the curtain, on the passerelle, he's doing a question-and-answer session with the audience, while choreographer Jerry Mitchell said, 'You gotta learn the dance, buddy let's go.' Gary Beach [who plays Georges' partner, Albin] and myself are learning the dance behind the show curtain with Jerry Mitchell while Harvey is out front."

In short order, Fierstein brought Hillner out, introduced him as "Gary's husband for the rest of the evening" and audience went crazy.

"It was one of those situations where you can do no wrong," Hillner admitted. "They're all with you. They love the fact that there's this drama happening in live theatre. I was in the cat-bird seat. I think I did really well — I didn't know I knew it as well as I did. I don't remember a moment of it, but I did two more performances that weekend and had a pretty good handle by Sunday."

Davis was ill again in January and Hillner played the role again for a week. On March 27, Davis was cut loose from the show, Goulet was announced to take over in mid-April and Hillner was the leading man in the meantime.

"The producers said, 'You're our guy — you're gonna be on,' and I went down and moved into the star dressing room," Hillner said. "It's been a great ride."

Ask any understudy and they'll probably tell you they don't want to go on in a role only once — they want it either never or they want it for enough performances to allow them comfort and connection with both the character and the cast. Rarely do understudies get the pleasure that Hillner has enjoyed.

To prepare for the role during previews, when he wasn't officially being rehearsed, Hillner brushed up on his own, as many understudies do.

"In general, you're on your own," he said. "You try to snag a rehearsal pianist when you can and go through the numbers and try to get as much out of it as you can. Maggie Torre, who is our second keyboardist, she was able to go through stuff with me. I learned phrasing and stuff from her, and a little bit Jim Laev, our associate conductor and occasionally from our conductor, Patrick Vaccariello.

"That's the nature of the beast and it's always been that way. You know what you're getting into. Anyone who says, 'I don't have any rehearsal, I'm not ready!' Well, guess what? You gotta learn it. You never know when you're gonna go on."

Hillner admitted to the pleasure of getting comfortable in the role, feeling it more deeply than he ever imagined he would.

"What becomes nice is that it gets in your bones," he said. "You get to work on the nuances, some of the pacing, some of the really, really finer points of the relationships. The who, what and where are taken care of. It's up to you to really connect and listen and be able to react to something different each time it comes at you, rather than think about 'Oh my God! What's my line?'"