Disclaimer: I do not own any of the characters of Arthur Conan Doyle, nor any of the various dramatic incarnations thereof. No profit is being made from this work.

Note: Welcome to this story! It's a crossover, so I think I'd better do a little bit of basic introduction for anyone less than familiar with one or both of the settings.

The Children's Academy of Dancing and Stage Training is a setting for many of Noel Streatfeild's books about children and the performing arts. It was established by one Madame Fidolia, formerly a star ballerina in the Russian Empire, who escaped to London after the Revolution. She founded the Academy probably sometime in the 1920s, initially as a ballet school. Over the years that Streatfeild wrote her books, the Academy evolved, transforming from a pure ballet school to a girls' all-around performing arts academy in the 1930s. By the 1940s, the Academy had gone co-ed and offered some academic classes. The last we hear of the Academy is in the early 1960s, when Madame is getting ready to retire, and the structure of the school has adjusted in other small ways. The Academy is shown to be a dynamic institution, changing with the times, and I've projected it forward a bit to see what might have become of it in the ensuing decades.

Sherlock Holmes has many skills and graces besides raw brain power. One might well wonder where and how he acquired some of those skills.

Finally, a note about the title. Streatfeild's first book for children was called Ballet Shoes. It was an enormous hit both in England and the United States. She gave her subsequent books interesting and unique titles, but her U.S. publishers retitled her books for publication in the U.S., probably for marketing reasons, to make them seem more like a series than they actually were. So Curtain Up became Theater Shoes, The Painted Garden became Movie Shoes, Wintle's Wonders became Dancing Shoes, and on and on. Following in that tradition, this story also has two titles. Enjoy it, and I'll see you at the end.

1. Old Boys Network

Something shrilled in John's ear. He reached out to swat in the vague direction of his alarm clock, but the noise did not stop. It was melodic, John's sleep-addled brain supplied. A moment later, he registered that he was hearing his mobile, which he had left on the bedside table – oh, Christ, earlier this morning, upon collapsing into bed following the conclusion of an intense case with Sherlock. For a moment, John considered letting the call go to voicemail, but then he considered that it might well be his locum agency telling him that he had a job. He snaked one arm from beneath the covers and grabbed the mobile, squinting at the screen. There was no name, but the number was a familiar one.

"H'lo, Mycroft," John mumbled.

"Tell my brother to answer his phone," Mycroft's voice crackled in his ear. "I've been trying to reach him."

John swiped a hand over his eyes. "'m not your brother's keeper."

"Yes, you are. Have him ring me. Tell him that the Academy wishes to speak with him. And that Madame will be highly displeased if he declines." There was a click as the call ended.

John stared at the mobile for a moment, and then flopped back onto his pillow. Well, there was nothing for it. Mycroft was not above pestering John if pestering Sherlock brought no results. He hauled himself out of bed, stretched, scratched himself, and then stumped down the stairs to the main flat. The kettle sang its siren song, and John filled it and switched it on before he went any further, setting up a little reward for himself for getting out of bed to run Mycroft's errands for him. He headed down the short hall and knocked on Sherlock's door. "Sherlock, wake up."

There was a pause, and then John heard an indeterminate grunt from the other side of the door.

"Sherlock, I know Mycroft's been trying to ring you. He's started in on me now. He said that some place called the Academy wants to talk to you, and that Madame will be displeased. Please tell me you haven't gone and insulted your grandmother or something."

John heard a swish and a thump, and then the door opened, and Sherlock's sleepy face, crowned with wildly tousled hair, appeared before him. "You said the Academy?"

"Yup. 'S what Mycroft told me. You ring him. Or ring them. I'm going to go make tea." John shuffled back into the kitchen, where the kettle chugged invitingly away.

John was halfway through his tea when Sherlock reappeared. "Morning," he said. "Want some tea?"

Sherlock shook his head. His expression was thoughtful, and he pulled his dressing gown tightly around his body. "I need to get dressed," he said, though he made no move to do so. "We need to go out soon."

"Mmm. Do we?"

Sherlock nodded. "I've just spoken with the Academy. They want to see me as soon as possible. And . . . I'd like to bring my doctor along."

The request was not delivered in Sherlock's usual imperious voice of command, and John glanced up. Sherlock looked unusually puzzled, but John could not tell if it was from simple lack of sleep or some deeper cause. "All right," he said. "Go get yourself cleaned up. I'll finish my tea and take the next shower. Can it wait that long?"

Sherlock nodded, and went off to shower.

The oddity of the day only increased when Sherlock elected to travel by Tube rather than by cab. John held his tongue until they changed at King's Cross. "This is a bit much, just to get to Russell Square," he said.

"You're the one who always complains about taxi fare," Sherlock said. "And . . . I rather like the Russell Square station."

Ah. Well, John was certainly not about to argue with that. He turned his face to hide his smile, and followed Sherlock onto the Piccadilly Line.

They disembarked, and Sherlock led them from the station to Russell Square itself. Their destination was an institution near the University of London. The institution appeared to take up three of the terraced houses that faced the Square, for the words "Children's Academy of Dancing and Stage Training" could be seen in faded gold paint spanning three doors. Near the first door was a newer brass plaque that read, "Fidolia Academy of the Performing Arts," above an engraved pair of ballet shoes with intertwining ribbons.

"We're investigating a ballet school?" John asked. "What, have we got a serial killer who goes after ballerinas?"

"I hope not."

Sherlock hesitated a moment, and then opened the door. The interior of the school had a peculiar odour, of wood and sweat, and something sweet and slightly spicy as well. Sherlock appeared to know exactly where he was going, and John followed him into a waiting room whose walls were filled with photographs of children in costumes. Some of them were signed. Most were relatively new, from the 1960s or later, but off in a corner, John spotted a few much older photographs that he thought might be from the 1920s and 1930s.

He was particularly struck by a faded photograph of a little blonde girl dressed as Alice in Wonderland, wearing black ballet shoes. The photograph was brown and crumbly at the edges, but the inscription could still be read. "With much love to dear Madame. Pauline." John recalled that Mycroft had mentioned a "Madame," but surely this could not be the same person, not if that photograph was as old as it looked.

Sherlock was speaking quietly to the young woman at the receptionist's desk. She smiled and nodded at him, and then rose from her chair and left the waiting room. Sherlock came to look over John's shoulders. "Former pupils of the Academy," he said.

"So I gathered."

John moved along to some of the newer photographs. Some were portraits, but some showed groups, and he found that he could guess at the way the school had developed from the types of groups that appeared on the walls. By the late 1970s, some of the groups appeared to be ballroom dance classes, to judge by the stiff posture of the children and the ugly "best" clothes that John remembered from his own childhood. There were also a few photographs of boys and girls in a gymnasium. As he looked through the photographs from the 1980s, he thought he saw something familiar in one small, unsmiling face. But just as he leaned in more closely to investigate, the door to the waiting room opened.

The woman who entered was about his own age, small and slender, her hair pulled into a bun on top of her head. She wore a plain black leotard with warm-up trousers pulled over it, and soft lace-up shoes on her feet.

Sherlock startled a bit when he saw her, and he inclined his head almost shyly, but the woman laughed. "Oh, there's no need for that."

"It's not done any more?" Sherlock asked.

"It is, but, well, you were never one of mine. It seems a bit silly, especially with what I've asked of you."

Sherlock gave an awkward half-smile instead. John took another glance at a photograph of a ballroom class from the early 1980s and sucked in a breath. He turned to Sherlock. "You were a student here?"

"A few classes. Mummy thought this school was better for me than the one where Mycroft had his dancing lessons." Sherlock focussed his attention on the woman. "You're the current administrator, I assume?"

"Yes. Dorothy Robinson." She advanced and held out a hand to Sherlock. "And you must be Sherlock Holmes. We still have a photo of you in our files, but you've changed since then." She turned her attention to John and raised a delicate eyebrow at him.

John put on his "meeting a new patient" smile and shook her hand. "Doctor John Watson."

Ms. Robinson's smile faltered just a little. "Oh, dear. I hope we won't need a doctor."

"We'll see about that," Sherlock said. "What's happened? All I was told was that it has to do with – with Madame."

Ms. Robinson nodded. "Come with me. We'll talk in my office."

She led them down a corridor lined with doors. One or two were open, and John could see dance studios lined with mirrors. The walls held corkboards and fire extinguishers, and one wall bore a small, empty glass case. Sherlock glanced at the case in passing, but said nothing. Ms. Robinson showed them into a room with the shiny wooden floor of a dance studio. One half of the room was lined with mirrors and a barre, and the other half had a desk and filing cabinets. Ms. Robinson sat at the desk and gestured to Sherlock and John that they should sit in the two visitors' chairs.

She took a deep breath and pressed her fingers against her eyes for a moment. "Madame," she said, "is gone."

Sherlock sucked in a breath. "Dead?" he asked. "No, of course not. You wouldn't have called me if she were. What do you mean, gone?"

"Wait," John broke in. "Before we go any further. Who is this Madame?"

"Madame," Ms. Robinson said. "Posina Fidolia. The owner of the school – well, the current owner. Inherited it from the previous Madame Fidolia."

"Her mother?"

"Her teacher." Ms. Robinson smiled. "Posina Fidolia is the greatest ballerina England has ever produced, and she trained here as a child. The first Madame Fidolia had no children, so her prize student took over the school in 1974. She renamed it the Fidolia Academy in honour of her teacher."

John nodded. "And, now what? Does she teach?"

"She used to," Ms. Robinson said. "She taught me. But she mostly retired from teaching years ago. She's very spry for eighty-eight, but she's been on oxygen recently, and she's just not able to teach full classes any more. Sometimes she does individual tutoring, with a pupil she finds promising, but even that . . . well, her hearing's started to go, and it's hard to teach dancing if you can't hear the music."

Sherlock frowned. "She's going deaf?"

Ms. Robinson nodded. "I tried her mobile this morning, and she didn't respond. At first, I thought she just hadn't heard it, so I went to check on her."

"Where?"

"She has a set of rooms in the upper floors," Ms. Robinson said. A faint, nostalgic smile flitted across her face. "Even after she turned the day-to-day of the school over to me, she wouldn't go anywhere else. 'Why should I stay anywhere else, Dorothy?' she said to me. 'Everything I love best in life is here.' We had an old studio on the top floor converted into a little flat for her."

Sherlock nodded. "And this morning?"

"I didn't hear her when I came in. She likes to do her exercises in the morning, but she's so deaf now that she turns the volume of her music up as high as it can go. Usually, it echoes through the whole building, but I didn't hear it this morning. I got worried, and I went up to check on her."

"What did you find?"

Ms. Robinson trembled, and John fished in his pocket for a packet of tissues and handed one to her. She smiled at him and blew her nose before she spoke again. "The door was locked, and I had to break in. And she was just . . . gone. Nowhere to be seen. The bed was perfectly made. It was almost as though she'd stepped out for a moment. But . . . she's an old lady, and her life was here. Where would she have gone overnight?"

John waited for Sherlock to start deducing the solution to the problem, but Sherlock was oddly quiet. Treasuring a rare moment to ask a question, John leaned forward. "Ms. Robinson. I'm sorry to have to ask this, but had you noticed anything . . . well, odd about Madame recently? Had she been behaving strangely?"

"What do you mean, strangely? She's never been an ordinary person."

"Geniuses rarely are," Sherlock murmured.

John glanced at Sherlock, but Sherlock pretended that he hadn't spoken. "Has she been forgetful?" John asked "Or confused? Have you noticed any changes in her personality or in the way she interacted with people?"

Ms. Robinson opened her mouth, but Sherlock interrupted. "Or, alternatively. Has she seemed fearful? Cautious? Might someone have been watching her?"

Ms. Robinson glanced from John to Sherlock and back again. "No. She seemed very much like herself. Only . . . well, more so."

"How do you mean?" John asked.

"Well, the students she was tutoring. One of them came to me and said that Madame had spent their entire lesson telling her stories; she didn't say what sort. And Madame has been visiting the senior ballet classes more frequently. She doesn't take them over, and she always seems to know where she is, if that's what you're worried about. She just . . . visits. Watches the students. If you ask her, she'll correct them, but mostly, she just watches."

John sat back in his chair. Never having met Madame, he couldn't be sure, but she didn't sound like a case of dementia. And, to be honest, he had no idea how much of her behaviour was her own personality and how much might be something new and frightening.

Sherlock had begun to fidget, drumming his fingers on his thighs and tapping his toes. Finally, he sprang to his feet, wearing the very particular scowl that he wore only when he was nervous and trying to hide it. "The exhibit case," he said.

Ms. Robinson blinked at him. "Sorry?"

"The exhibit case, out in the corridor. It used to contain a pair of antique ballet shoes. Where are they?"

"Oh." Ms. Robinson rose and sorted through some files. "They were removed for cleaning. That was . . . a week ago, perhaps?" She consulted a piece of paper. "We sent them to a costume restoration house in Covent Garden. Why? Is that important?"

Sherlock's expression was shuttered. "It might be. Everything is important in some way. Yes, the shoes are important. How can the world be so full of idiots?"

John put a hand on Sherlock's arm, and Sherlock took a deep breath. "Show me her flat. Show me where Madame lived."