Aramis walked through the quiet streets with Joan by his side, her face and body completely covered by a grey cloak with a large hood. He led the way to the broad and elegant streets that had been laid out according to King Louis's plans for a glorious new Paris.

Turning the final corner, he heard music. A harpsichord being played by a master, a rippling cascade of intricate harmonies. He smiled, remembering those long-ago evenings by the fireside at his parent's home, when he had first learned to love music. He walked up to the smart, freshly painted door and knocked gently.

The music stopped. A few moments later, the door opened, revealing a slim elegant young man wearing plain but fashionable clothes.

"William, it's wonderful to see you," said Aramis. "I apologise for the hour, but I need to ask a great favour. May we come in?"

William stood in the doorway, his face troubled. He stared at Aramis for a moment, then shrugged slightly, turned, and let them follow him upstairs.

The main chamber of William's apartment was exactly as Aramis remembered; teetering piles of sheet music heaped in odd corners, lovingly polished musical instruments carefully placed on shelves and tables. A harp stood in one corner, and a magnificent harpsichord had pride of place by the window. As a sort of grudging afterthought, a couple of chairs and a low plain table stood by the fireplace for the rare visitors who were allowed to enter William's home.

William stood in the middle of the room, his weight shifting from foot to foot, rubbing the knuckles of his left hand with the callused fingers of his right. Aramis hadn't seen that gesture for years, and felt a twinge of guilt – these days he normally saw William at Court, completely absorbed in his music. It made it far too easy to forget the strain on William's nerves of maintaining such a perfect mask for so many years.

Joan was looking at Aramis and William in turn, confused and looking as though she was starting to get a little frightened. He had promised her a disguise, and brought her here with no explanation. Lurid tales of what happened to good girls lost in the wicked streets of Paris were doubtless preying on her mind.

"William, this is Joan — I'm afraid I can't give you her full name. Joan, this is William Thornton, one of the finest musicians in Paris."

Good manners prevailed, as they almost always did. William bowed gracefully, and Joan bobbed a nervous curtsey in response.

"William, Joan has put herself in grave danger in His Majesty's service." Best to lay it on thick in such circumstances, and an appeal to patriotism was always a good start. "We need to get her out of Paris at dawn, without anyone recognising her. Can you help?"

William hesitated.

"I'm sorry. I wish I could have come to you first, asked you in private. But there was no time." Aramis pleaded.

William sighed, then turned his attention to Joan. "May I take your cloak Madame?"

Having relieved Joan of the bulky cloak, William looked Joan up and down, making her even more nervous than she had been before. Aramis watched as his friend assessed Joan, considering her face, her height, the width of her shoulders, her figure. He remembered doing the same thing himself, to another young woman, so long ago now.

"I can help," said William.

"Thank you," said Aramis. He hadn't relished the idea of going back to the others and admitting his disguise scheme had come to nothing.

"Joan," he said. "William will lend you a suit of clothes, and help you dress yourself as a boy."

She stared at him, open mouthed with shock. "It will never work. I can't…"

"Oh, it will work," said William "People see what they expect. Breeches and a coat make you a man."

Joan turned and looked at William. At his slight frame, smooth skin and soft jawline. William smiled. "It's worked for me for seven years now."

As William (always William, forget Celeste had ever been) led Joan to the bedroom to help her dress, Aramis settled down in one of the chairs to wait. Odd snatches of conversation came from behind the closed door.

"I can't breathe!"

"It needs to be tighter, or the coat won't hang properly."

"Why do they wear this?"

"Keep your head up."

"Ouch!"

"Have a look in the mirror, see what you think."

"I'm not sure. I don't look myself, I suppose."

"Don't have your hands like that. Keep them by your sides."

The bedroom door opened at last and William emerged, looking much more relaxed. Behind him was... It was hard to judge really. Aramis knew the secret after all, and that made it almost impossible to see what an ordinary observer would. The clothes were good – William had great experience there of course. It was the posture, the movement and gestures that didn't quite fit. Still, all they needed was something that would pass at a casual glance as they rode past. She would do.

An hour later, Aramis walked Joan back to the garrison, carrying a bag containing her tattered dress and corset. Joan walked awkwardly in the unfamiliar clothes. To be fair though, the one time he'd had to wear a skirt and corsets (an adventure he had decided never to mention to his friends), he'd barely been able to breathe, let alone walk.

"How did you and William meet?" she asked, almost as soon as they had left the apartment. An inevitable question, he supposed.

"He – always he, even in my head, to stop careless mistakes – is my cousin. He always loved music. When we were children, he learned to play every instrument he could lay his hands on, memorised every piece of music. I used to spend hours listening to him play. It was all he ever thought about, cared about, his whole life. But of course once he turned fifteen, his parents' thoughts turned to marriage. They were kind, they only wanted to do their best, their duty as they saw it, but William grew more and more distressed. All their talk of a husband, children, running a home; they might as well have proposed a lifetime in prison. We'd always been close, only a few months apart in age, and she, he, confided in me. In the end, he decided to run away. I helped to stage an elopement with a fictitious lover, and helped William to find lodgings and contacts with musicians in Paris. Once people heard him play, that part was simple at least."

"And is he happy?"

"Yes, of that, I'm certain. His talent, his genius is a truly a gift from God. It would be a sin to let it wither away in some country manor. Every few months, he writes to his parents. I send the letters, when I'm away from Paris so they can't be traced back to him."

"And no one has ever guessed?"

"No. His profession helps. No one expects a musician to be a hulking great brute of a man. And he claims to be English—everyone knows they're a bit peculiar. The illusion is easier to maintain in a salon than it would be on the streets."

They turned the corner and drew close to the garrison gate. Joan put her hand on Aramis's arm.

"Thank you for helping me, and for trusting me," she said.

"You are most welcome," he replied. "I suggest you sleep in the shirt and breeches tonight. They'll look more convincing with a few creases. Goodnight."

He stood in the yard and watched to make sure she got safely back to the guest room she was sharing with the children, then headed for his own bed. He could get maybe five hours sleep before breakfast.