"Will you stop fidgeting?" Aloysia sighed.

Constance dropped her mask back into place with a scowl. "These feathers itch."

"Don't be insufferable," Aloysia said, regally smoothing her skirt across her lap with a gloved arm.

Constance frowned up at her sister, though from her seat at her side it was hard to take in the entirety of her costume. Aloysia was in a ridiculous green gown adorned with long black feathers that matched her own mask, with her hair piled neatly atop her head. The skirt was just full enough to hide the subtle bulge of her stomach. In another month Aloysia wouldn't be able to leave her house anymore, not until after the baby came. If this was to be her last night out, of course she had had to make sure that she was in the grandest costume of any of them. Constance was supposed to be dressed as a white dove, but she felt like a common sparrow at her sister's side. "I still don't know why you're forcing me to come with you."

Aloysia just smiled haughtily at her.

From the other corner of the carriage, Antonio Salieri grumbled, "Nor do I."

"You'll thank me," said Aloysia, and that was clearly all she intended to tell either of them.

Salieri's eyes met Constance's for a moment and he grimaced good-naturedly before tying his own mask back into place. Constance quickly turned to look out the window. She didn't dislike Aloysia's friend, but there was still something strange about seeing the court composer outside of the context of an opera house. She also wasn't sure if he knew that Constance knew that Aloysia wasn't actually his mistress. That the baby that most of Vienna thought was Salieri's was actually her husband's. Constance and Aloysia had shared a room when they were little: even now that Aloysia's marriage had separated them, there wasn't much that the sisters kept from each other.

That was why it was so unusual for Aloysia to refuse to tell either of them why she had insisted they accompany her to a masked ball that night. Constance was unaccustomed to being on this end of one of Aloysia's schemes.

"Are we supposed to be recognizable?" Salieri asked, gesturing toward his ornate mask.

"It doesn't matter. I'll make the introductions."

"Will we both be meeting the same person?" ventured Constance.

Aloysia didn't deign to answer.

Salieri flopped back against the seat with his arms crossed. "If Rosenberg or any of his friends see me like this, I might as well throw myself into the river."

Aloysia swatted at Salieri's leg, chiding, "Antonio! Don't talk like that in front of our baby!" and placed a hand over her belly.

On either side of his mask, Salieri's ears turned red. "I told you not to joke about that," he muttered, sneaking a glance at Constance. "It isn't funny."

"Neither was what you said!" Aloysia retorted.

Constance pointedly turned back to the window. It really wasn't any of her business.

"What do you think? Does it suit me?" Wolfgang asked, and when Nannerl looked up to answer it took all her reserve not to laugh out loud. Her brother was modeling his costume in the doorway, the fine silks and tufts of tulle cutting a stark contrast to the sparse servants' quarters where Colloredo was having them stay while they were in Vienna.

"Well, I certainly doubt anyone will recognize you," Nannerl said.

"No?" Wolfgang beamed. "I bet I can still find someone to bring back with me, even dressed like this!"

"Can you?"

"Absolutely," said Wolfgang, prancing about on the landing and pretending to curtsy to an invisible dance partner. "Want to make a wager?"

"Alright. Whoever comes home alone has to dress like this at the concert next week, too. But without the mask!"

"It's a wager." Nannerl shook his hand, biting back her grin until he turned away. Wolfgang had no idea what was in store for him.

The ball to which they had been invited was a lavish affair at the outskirts of town, hosted by a widow who was the last survivor of an old title. With no heir to her famous fortune, the rumor was that she had decided to waste it as spectacularly as possible. So many guests had been invited that their carriage had to stop nearly a mile away in the middle of the forest, rolling forward a few feet at a time while group after group disembarked up ahead. Nannerl readjusted her mask self-consciously. At a masquerade, it would be impossible to tell the nobility from the commoners, or the rich from the working class. Was a costume rented or dingy from disuse? Was that a duke disguised as a beggar? Were these two of Colloredo's employees or members of the imperial court? It would be difficult to say. When Nannerl and her brother finally alighted from their carriage, they blended into the colorful crowd like two more blooms in an overgrown garden.

The ballroom was breathtaking: silk skirts and gilded shoes were packed tightly over the marble floors, crystals dripped from the ornate chandeliers overhead, and distant paintings adorning the ceiling seemed bemused by the costumed horde pouring in from the frosty night. Wolfgang seized her hand and pulled her through the crowd, leaving her scrambling to avoid treading on the other invitees' dresses or feet, mumbling apologies as she collided with guest after guest, until finally they had joined the group of spectators who were pressed in around the quintet of musicians at the far corner of the ballroom. While Wolfgang muttered to her about the pace of the song they had chosen and the form of the conductor, Nannerl rocked up onto her toes and scanned the crowd.

A hush fell over the room when their host was announced. She appeared at the top of the stairs dressed as Venus, with a stuffed dove affixed to one shoulder and a sparrow on the other, and the guests applauded as she called upon the musicians to begin the first dance.

"Shall we?" Wolfgang asked with a grin. "I doubt the orchestra will let me lead them dressed like this, so we might as well enjoy their sloppy playing as best as we can."

They were both out of practice, but the dance was an easy one: it was stiff and formal, giving Nannerl a chance to scan the rest of the crowd and Wolfgang time to figure out how to move without his feet tangling in his heavy costume. The second time he tripped, he grumbled, "We could have just come as ourselves, you know. There are enough people here that no one would have minded."

Nannerl just nodded, though behind her mask she was beaming. A tall, elegant woman in a green gown laced with long black feathers had just joined the dance. Her partner was just shorter than she, a well-dressed man with gleaming hair and a neat beard visible at the bottom of his mask. They were just as the letters had described them.

A waltz began, and a new surge of couples filled the floor, separating Nannerl and Wolfgang from the other pair. She gritted her teeth and tugged her brother back toward that side of the room, scanning for those two dark costumes among the jewels and pastel silks that adorned the other guests.

This had to work. For Wolfgang's sake. For the sake of his music.

The first letter had been unsigned and had been waiting when they arrived in Vienna, addressed only to "Wolfgang Mozart's sister". There had been a brief outline of the scheme and the instruction that if she was willing to participate she should leave a handkerchief hanging from her window that would be visible from the street below. Nannerl had done so enthusiastically, and had practically pounced upon the second letter when it was delivered the following morning. This was exactly the inspiration that her brother needed. These three years since he had come home to Salzburg, he had been a shadow of the musician Nannerl had always known. If only one of them was going to be able to compose, then Nannerl would do whatever it took to make sure that Wolfgang was writing to his full potential. He needed a muse, and the author of the letters knew someone who needed Wolfgang just as badly.

The next time Nannerl and Wolfgang waltzed past the dark couple, the woman in the feathered gown caught Nannerl's eye. She nodded, and Nannerl nodded back over Wolfgang's shoulder. So this was the famous Aloysia Weber. From that quick glance to the manner of her dress to the way she held herself against her partner, she was everything Nannerl had imagined she would be. No wonder Wolfgang had been enchanted by her all those years ago.

The current of the dancers shifted, bringing Aloysia and her partner back toward Nannerl and Wolfgang. Their eyes met again, but this time Nannerl released her brother and stepped back; this time Aloysia swung her partner a little too hard, and the man in black staggered across the floor into Wolfgang's arms. Wolfgang let out a startled giggle as he caught him, and before either of their partners could return to them Aloysia seized Nannerl by the wrist and spun her away. "Nannerl, I presume?" Aloysia purred.

Nannerl grinned. "That went better than I expected."

Half an hour into the masquerade ball, and Constance found herself leaning uncomfortably against the wall and tersely shaking her head at any gentleman who tried to approach her. Aloysia had dragged poor Salieri off into a dance the moment the music had started, promising Constance that she would be back and Constance would thank her. Salieri had shot her one last pitiful look over Aloysia's shoulder as they left. That had been two songs ago.

It wasn't that Constance hated dancing necessarily, or that she hated the thought of flirting with an anonymous stranger at an opulent masked ball. She was just frustrated by it all. Every suitor her mother had pushed in her direction had been the same: coarse, crass, and oblivious, looking at her like a trophy rather than taking an interest in who she was. The reality of men had turned out to be nothing like the stories she had heard when she was a child. How was she supposed to stand for it? She couldn't bear the thought of throwing her freedom away as Aloysia had done, of replacing her name with someone else's, of giving up the person she had always been in order to run a house and bear children. It wasn't worth it, not for a clumsy kiss and rough hands on her skin. Not for foul breath against her neck or the weight of a man atop her as Aloysia had described. She had seen her sister's lip curl when she talked about her husband. Constance's skin crawled at the thought of it.

And yet, there were times-alone in her room, of course, when the house had fallen still-that she tried to imagine something better, softer: a light touch, soft lips, a tender embrace. She had started to admit it once or twice to Aloysia, but it was hard to put to words. It was embarrassing. What was she to say? "Your husband sounds terrible, Aloysia; I hope I find someone gentler"? Out of the question. They were thoughts she would have to keep inside herself.

She had studied the bearing of the few men who tried to coax her into the dance, but none of them were quite right. Their shoulders were too broad, their jaws too square, their hands too big. She declined each time, crossing her arms tighter and tighter over her chest.

And then Aloysia came back in a flurry of laughter and feathers, and she was no longer with Salieri but with a small, slight stranger in an ill-fitting lavender jacket. Constance straightened up, tugging her feathery skirt into place. "Aloysia?"

"Constance, my dear sister!" Aloysia said grandly.

"Where's Maestro Salieri?"

The stranger let out a delicate giggle and clapped a little hand over the mouth of their grinning mask.

"The maestro has had an unexpected change of partner," Aloysia said, slinging an arm around Constance's shoulders and drawing her forward. She pointed out at the floor. "Look!"

There was Salieri in his fine black suit, his hair gleaming in the candlelight and his mask failing to hide that his ears were bright red. His hands were planted rather uncertainly at the hips of a dancer in an overworked blue gown adorned with glimmering butterflies. His partner's arms were wound around his neck; neither of them seemed to have any idea which was leading and which was following, much to the consternation of the couples around them.

"Who is that?" Constance asked.

"My brother," Aloysia's new partner replied, stretching out one of those small hands. "You're Constance, right? I'm Nannerl."

Constance took the hand uncertainly, searching the large brown eyes she could see on the other side of the grinning mask. "But you're- are you a woman?"

Nannerl laughed again, and for some reason the sound coursed through Constance's chest like a spark of lightning. Nannerl didn't let go of her hand. "Come on," she said to both of them, "let's get out of here."

"I'll stay a little longer," Aloysia said, and Constance saw the glimmer of a smile behind her mask. "You two go. Take Salieri's carriage. That will keep him from fleeing the scene if he finds out who his partner is."

"Perfect!" exclaimed Nannerl. She turned her shining eyes back toward Constance. "Shall we?"

Finding that her voice had suddenly abandoned her, Constance could only nod.

If Aloysia Weber had been everything Nannerl had expected, then her sister Constance was more than Nannerl could have dreamed. She was golden hair and bright blue eyes in a shining white dress, soft shoulders and rosy lips, work-worn hands and flushing cheeks. Nannerl couldn't bear the thought of releasing her hand, and Constance had yet to pull away. "Which carriage is Salieri's?" Nannerl asked, and the shy smile that spread across Constance's lips made her heart hurt.

"This was Aloysia's plan?" Constance asked once they had spoken to a footman and were waiting out into the frosty courtyard. "Send Salieri off to dance with your brother while you and I steal his carriage? I don't understand."

"Apparently the maestro needed a push," said Nannerl. "A literal one."

"Alright," Constance said, but the crease didn't disappear from between her brows. A handsome black carriage had just pulled around to the front of the drive, and Constance released Nannerl's hand at last to go speak to the driver. He must have been fine with whatever instruction Constance gave him, for a moment later she turned to Nannerl and smiled so brightly that it warmed the night air around her.

Mindful that she was dressed as a man, Nannerl helped Constance up into the carriage and clambered in after her, taking the seat at her side. "Where did you tell him we're going?"

"Just back into town," answered Constance. "I wasn't sure if you and I were supposed to- I mean, does Aloysia expect us to go to the same place? It's too late for dinner."

"We've only been in Vienna a week," said Nannerl. "I'm afraid I don't know anywhere to go but our lodgings." She removed her hat and mask, shaking her hair loose until the long brown curls fell around her shoulders. When she looked up again, even in the dim carriage she could see that Constance's cheeks had gone pink beneath her white domino mask. "Are you alright?"

"Just-" Constance's eyes darted nervously toward Nannerl, then back down to her lap. "I don't know. I knew you were a woman, but I didn't expect you to be so..."

Nannerl waited a beat. When it became obvious that Constance wasn't going to finish the sentence, she suggested, "Feminine?"

"Pretty," Constance mumbled.

A fist seemed to close over Nannerl's heart. She took a deep breath to steady herself. "I'll admit, I thought the same thing when your sister introduced me to you."

Constance glanced up, wide-eyed, and turned away again. But then she slid her hand across the seat between them, letting her fingers brush over Nannerl's.

The touch sang through Nannerl's veins, bringing a rare heat to her cheeks. She waited until Constance looked up at her through her thick lashes. "I think- that is, if you don't mind- I think I might need a push too," Constance said quietly.

Nannerl laced their fingers together and brought Constance's knuckles to her lips.

From the first touch of Nannerl's soft lips to her skin, Constance's pulse began thudding through her ears like a drum. How could this woman, practically a stranger, have seen with a glance the secret Constance hadn't yet dared to put to words? How had Aloysia known enough to find her, to bring them together? But if they had sent Salieri dancing off with another man, then maybe-

Nannerl turned Constance's hand over and pressed another kiss to her palm; Constance shivered, and she looked up at her with a grin. "Is this the kind of push you meant?" she asked.

Constance grazed the fingertips of her free hand along one of Nannerl's long curls and nodded, not quite daring to reach for her. "You don't mind?"

"Mind? Do I mind holding the hand of a beautiful stranger? Don't be silly."

"I meant- I mean, sometimes I've wondered- but I didn't think anybody else would- do you... can we-?"

Nannerl closed the distance between them, slid off Constance's mask, and caught her lips in a long, slow kiss. The heat of her mouth, the weight of her body as she leaned into Constance, the tickle of her breath against Constance's cheek-nothing had ever shaken her so deeply before. "My lovely Constance," she murmured when she broke away. "I would do anything to you that you asked."

Constance heard herself make a noise that was more whimper than sigh, but had no time to be embarrassed about it before Nannerl kissed her again.

Nannerl awoke to the sound of a creaking floorboard in the hallway punctuated by one of her brother's breathy giggles. She slipped out of bed, pulled on a housecoat, and cracked open the door just in time to see him press Salieri the door of his room with a sloppy kiss. After they broke apart, the visibly-flustered court composer managed to work the door open and staggered backward into Wolfgang's room, shucking off his jacket and loosening his cravat as he disappeared from Nannerl's line of vision. But Wolfgang looked up and caught her eye before he followed him. "I hope you found those breeches comfortable!" he whispered theatrically. "As you can see, I'll be returning your dress to you in the morning!"

Nannerl stepped back into her room long enough to retrieve Wolfgang's lavender jacket from the floor and tossed it to him. "I'm afraid neither of us lost the wager," she shot back, and then she pulled her door closed with a wink.

Constance sat up in Nannerl's bed with the sheet clutched over her breasts, starlight threading through her waves of golden hair. "Who was it?" she whispered.

"Just my brother," Nannerl said, slipping out of the housecoat and dropping a kiss onto Constance's forehead. Constance leaned into her touch, sliding her arms around Nannerl's waist and pulling her down onto the bed next to her. "I could introduce you in the morning, if you'd like."

"Don't bother," answered Constance sleepily. "I'm tired of being introduced to men."

"Good," Nannerl said. "I'll keep you to myself." She kissed Constance's cheek and nestled into her warm arms.

If she could ever force herself to leave this bed, she would have to remember to thank Aloysia Weber.