A/N: This story assumes all of the facts laid out in Leroux's novel, stopping short of Erik's death. Thanks to EspoirDio for the masked ball prompt!

It was Mardi Gras, and it took Clara all of ten seconds inside the Paris opera house to understand why she had long been forbidden to attend its masked balls.

This one had started at midnight. She had arrived at only half past, yet gone was the sense of decorum that she expected of social functions; in its place was merry chaos. Alcohol flowed freely. Patrons were raucous and bawdy, doling out catcalls and playful insults. Costume dresses were snug and low-cut. Thousands of people were packed into the building like well-dressed cattle, and one could barely walk three paces without being jostled. All of this, and she had yet to set foot beyond the grand vestibule at the front of the building.

Beside her stood her sister, Margot, and their aunt. Aunt Céleste surveyed the scene with measured calm, perhaps for the benefit of her uncertain nieces. A masquerade novice herself despite her years, she was attired in a Renaissance-style gown of emerald velvet and puffed gold satin, with a coordinating gold mask. "Come, girls, let us go to the loge," she said.

The three women pressed through the crowd to reach second-tier box nineteen, which they shared with their cousins the Beaumonts. Even the corridor outside of it swarmed thickly with guests. Following closely behind her aunt, Clara pushed past the mahogany door of box nineteen and into the sanctuary of its little carpeted salon, hung with red damask silk.

She had not yet recovered from sensory overload before her sister impatiently parted the curtains that separated the salon from the box seats overlooking the auditorium. "Oh, do come look!" Margot cried.

With some hesitation, Clara and her aunt peered over the loge balcony to observe the crush of dancers and revelers in the rich gold-and-crimson auditorium below. Every last seat had been removed from the floor for the occasion. The orchestra played a lively quadrille from the pit, but the crowd was packed too tightly to allow space for the dance—though that did not stop several inebriated couples from trying. Guests were costumed as harlequins, dominoes, historical figures, shepherds and shepherdesses, various flora and fauna. There were even men dressed as women and women dressed as men. Clara had to admit that it was quite the spectacle, if one could overlook the undercurrent of debauchery.

Months before, when her father had announced to the family his intention to be away on business during Mardi Gras, Margot had been so cunning and subtle in planting and nursing the idea of the ball in her aunt's mind that Céleste may very well have believed she'd thought of it herself.

It had been five years since Aunt Céleste had seen both her elder son and her daughter married off, and ten since her husband and younger son had "gone to join the Lord in heaven," as she liked to say. Now she spent her days languishing in her brother's household, coming to terms with the fact that her nieces—whose upbringing she'd overseen since their mother died in childbirth—would soon marry and leave her without purpose.

"I am old," she had decreed one evening. Since the conclusion of supper she'd moved from wine to apple brandy, growing more candid with every sip. "I should like to see a bit more of this world before I leave it." She had then proposed that she escort Margot and Clara to the masked ball under the condition that "we never speak of this to your father."

It took much longer for Margot to persuade her sister to attend—months, in fact. The masked balls were not necessarily off limits to society women, especially with the option of disguise, but to attend an event known to cater to hedonism was to risk tarnishing the purity and reputation of one's family name.

Clara did not like risk. Risk was dangerous and unpredictable—a step off a ledge with no certainty of what lay below—and she had already led quite a comfortable existence without it, thank you very much. She had maintained her intention to stay home from the ball up until one week prior, when she was presented with the costume that Margot had commissioned for her.

The gown was black velvet swathed in gauzy midnight-blue tulle, which was covered with small stars of silver tinsel. For her waist, there was a silver belt of stars and a crescent moon in the center, just below her navel. The coordinating mask was dark blue velvet with cutouts shaped like cat-eyes; it was dotted asymmetrically with tiny silver stars, many of them clustered dramatically around the corners of the eye holes.

The ensemble had been too beautiful—too her—not to try it on.

As she'd stood before the mirror, admiring the contrast of caramel hair against inky velvet, her sister had said, "Well, that's settled. You must wear your hair down."

"I cannot," Clara had said, trying not to look wistful as she twisted her hips to make the stars swirl around her.

"Think of it as our last great sisterly adventure," Margot had replied. "Do it for me, at least."

The thought had been sobering. They were nearing their twenty-fourth birthday, and their father had decreed early in the year that he intended to see them married by Christmas. They had worn his patience thin, he'd said. Clara had already turned down a suitor because she did not care for him; Margot had rejected three because she cared for all of them—and more—and loathed the idea of chaining herself to one man forever.

"Fine," Clara had said, releasing an exaggerated sigh. "At least if I am somehow dishonored or murdered, I will not have to worry about finding a husband this year."

Margot had squealed and pulled her into a suffocating hug. "Do not forget what I said about your hair."

Clara was, in fact, wearing her hair down. It had taken a combination of sleeping in rags plus hours of fierce determination by her lady's maid, Juliette, in order to tease her stick-straight locks into thick ringlets that would hold for the night.

Margot's costume was another play on the sky, her skirt a light blue crinoline beneath sheer tulle that had been dyed to look like an arcing rainbow, with beading on the lower half to look like raindrops. There was a gold sunburst bodice and a matching headpiece for her honeyed brown updo. She studied the scene in the auditorium with an eagerness both characteristic of her and yet unmatched by any of her previous enthusiasm.

They were brought trays of champagne and oysters and petits-fours. Aunt Céleste, giving in too eagerly to the evening's libations, chattered at length. At one point, a masked man who quite resembled Monsieur Beaumont in physique and voice burst in with a supple gypsy girl on his arm, noted the box's occupants, and muttered an embarrassed apology before beating a hasty retreat.

An hour into their stay, Clara—still nursing her first glass of champagne—surveyed the boxes circling the auditorium and remarked, "How surprising that so many of the loges should be empty tonight."

"Only the box seats," said Margot. "You can see under the curtains that many of the salons are lit."

"Why stay in the salon and miss the ball?" Clara asked, pretending that she had not been tempted to do the very same thing.

Her sister smirked. "Have you no imagination, sissy? Think: if you were one of the many disguised, intoxicated guests throwing caution to the wind tonight, what might you want privacy for?"

Clara's eyes widened. "How vulgar!" she cried. "Where did you even hear such a thing?"

"Carole-Anne Yount. And she heard it from her brother, the crude one. It takes only a few sips of wine to loosen her tongue, you know, little bird that she is." Margot drained her second glass. "Also, I saw a half-dressed couple on the ground tier close their loge curtains. It's all very enlightening, wouldn't you say?"

Clara shook her head. "Sometimes I wonder whether you and I truly shared a womb."

"Funny, you never seem to doubt it when you remind me that you are the eldest by twelve minutes." Margot flashed her a teasing smile and stood, pulling Clara up from her chair. "Follow me. I am so bored in here." She led her sister by the hand into the salon, where their aunt sat flushed from alcohol, a half-eaten canapé pinched between her fingers. "Aunt Céleste, we are going exploring," she announced.

The elder woman nodded agreeably and waved them along. "Enjoy yourselves, dears," she said. "Make good decisions, and all that." She let out a small giggle and bit into the remainder of the hors d'oeuvre.

"That was easier than I expected," Margot chirped at the door.

"We cannot be seen without an escort!" Clara protested. "People will think us...kept women."

"Nonsense. No one knows or cares who we are at this point. You can be anyone you want to be tonight, sissy! Let's go and see what's happening in the grand foyer." With that, Margot pushed open the door, and they were swept into the crowd.

They were separated before they made it past the grand staircase, Clara losing sight of her sister among a sea of men in black top hats who flirted more ostentatiously with women than she had ever seen in her life. The building started to spin around her, and she gripped a balustrade in order to rein in her panic. She would continue to the foyer, she decided, believing Margot likely to do the same.

Music and voices melded into a steady thrum as she inched through the mob. She began to catch glimpses of things that she wished she hadn't seen: bodies pressed together, hands disappearing up skirts, flesh exposed and groped. The air was thick with the smell of cigars and sweat and alcohol and vomit, and as she pushed her way through the crowd, more than one hand palmed the curves of her body and she thought she might be sick. Her cheeks burned with mortification.

She was fighting back tears by the time she found the grand foyer, which was no less crowded. She knew that the doors along one side opened out to the loggia, a massive elevated terrace stretching the full length of the foyer, and she prayed that the crowd would be sparse enough outside to allow her fresh air and relative quiet.

But the windowed doors would not even open. She could see that the terrace was dark and empty, no doubt cordoned off to prevent drunken revelers from tumbling over the balcony, but still she rattled the handles, a panicked sob bubbling in her throat.

In a moment of weakness, she abandoned decorum and leaned resignedly against one of the hall's many gilted marble columns, gazing out at the throng of people. It was then that she saw what made her blood freeze.

It was a man—at least, he gave the outward appearance of being one. He was somewhat tall, quite thin, and dressed as a Spanish bullfighter. With his combination of cropped silk jacket and snug, tapered trousers—both a sultry garnet red, with thickly ornate gold embroidery—he was practically all legs: spindly, but striking. His accessories were black as night: the bulbous fur hat typical of matadors, a pair of slippers, a cloth mask that extended from forehead to lips. He wore no gloves, and his long fingers were almost skeletal in their thinness.

She could not articulate why, but there was something entirely otherworldly about him. Even as he stood still, his posture suggested something skulking and sinister. He seemed to exist on a plane apart from everyone else: a bad omen, personified. Clara's heart beat erratically; her skin prickled and turned to gooseflesh.

His eyes suddenly fixed on hers, and she could have sworn that they almost glowed rich amber in the shadow between the overhead chandeliers. She nearly stopped breathing entirely. And yet, despite her discomfort, she did not divert her gaze. Could not. She felt inexplicably drawn to him.

They continued to stare at each other. His expression remained almost impassive, if not mildly annoyed. And then, so slightly that she almost missed it, he cocked his head a few degrees to the left.

She shuddered, and then she must have blinked—for in the split second that followed, he had vanished. She scoured the foyer, but there was no sign of the ghostly matador.

A waiter bearing champagne walked past her, and she plucked a glass from his silver tray. Next to her was a small table of standing height, littered with empty glasses and hors d'oeuvres plates, and she set her gloves on it in order to partake of the alcohol. She drank too much, too fast, in a rush to soothe her nerves; the bubbly liquid was halfway gone before she came to her senses and switched to measured sips. She supposed that if she could not escape, she would at least rely on the alcohol to buoy her to that conversational sweet spot between sober and uninhibited. Her muscles released a bit of their tightness.

"Are you not enjoying yourself, mademoiselle?"

The words were quiet and clear despite the volume of the crowd, as though delivered a breath's length from her ear. She started, nearly spilling the remaining champagne down her dress.

It was a man's voice, soft and deep and resonant. Hypnotic. Somehow, even without visual confirmation, she knew whose it was. And despite the terror that seized her, she had the sense that she would have done anything the voice asked of her.

A/N: I can't take full credit for Clara's and Margot's costumes; they are based on ones that I have seen in pictures or drawings, Margot's in particular. Clara's is a blend of ideas.