Author's Note: This is not related to my other Sherlock/Harry Potter crossover. I was really excited about this when I first got the idea, but I've been going back and forth over whether or not I like it now that it's written. It's undergone a lot of editing, though, so please, please drop me a review and tell me what you think when you're done!

"John, could you put this book up for me?"

"Which book?"

"That one."

"Sherlock, you're not pointing or anything, I have no idea which of these dozen you're talking about," said John exasperatedly.

Sherlock sighed. "The one I just finished with, about the discoveries of slow-acting poisons and their effects."

"Oh, that one," said John sarcastically. "And no, put your own book up."

Sherlock looked up from the new book he'd just started to glare at John and saw that he was eyebrow-deep in Astronomy homework, the part of his face left exposed mirroring Sherlock's own stormy expression. No wonder he was more snappy than usual. Sherlock didn't bother returning the book to its proper shelf; Madam Pince or the house elves or whoever could deal with it later.

"Do you know how many moons Jupiter has?" asked John a moment later, his voice slightly worried. Sherlock didn't answer.

"Sherlock?" John prompted. "Sherlock, I'm talking to you."

"Yes, blessed with extraordinary observation skills as I am, I had noticed that," said Sherlock, annoyed.

"So you just decided to ignore me?" asked John, bristling and sounding slightly wounded.

"I don't know how many moons Jupiter has, John," said Sherlock. "You'll remember that I dropped Astronomy to fit in Arithmancy last year."

"Yes, I'm bloody well reminded of that whenever Professor Sinistra sets and essay as bad as this!" hissed back John over the piles of books and parchment spread out on their table. "Pass me that map of the solar system."

"No," said Sherlock shortly, turning a page of his book.

"Pass me the map, please," growled John.

"No," insisted Sherlock stubbornly. "You refused to help me, I won't help you." He thought he'd been extremely tolerant up until now—there was an itch on his shoulder he hadn't asked John to scratch, and he hadn't complained about the overly-loud scraping of John's quill for the past half hour.

"Sherlock," said John, raising his voice in frustration. "Maybe you need to get off your arse sometimes and realize that—"

Immediately drawn by the volume of his voice in her precious library, Madam Pince swooped down upon the pair of them like a gaunt and starved bird of prey, screeching at them to get out and accusing them of disturbing the studious caverns of her forefathers with their blasphemous bickering.

Naturally, Sherlock and John rushed for the door as fast as they could while trying to collect their things, John swearing vehemently once they were out of her earshot.

"Great, Sherlock, now I have to finish that essay without all the books I was using, and I wanted to do it tonight because of the Quidditch match tomorrow! You're not even coming, are you?"

Sherlock fastened the clasp on his bag. "Of course not, there will be people there. You know how much I detest having so much of the school around me."

John sighed, clearly not done being angry with Sherlock. Sherlock couldn't help but have his attention drawn to the way the light from the window behind him was lighting up John's hair, almost as if he had been bestowed a halo of sunlight. His friend didn't know that he had never missed a single one of his Quidditch matches.

"Well, I'll see you around, Sherlock," said John, turning and leaving in the direction of the Gryffindor common room. Sherlock watched him go, staring at his retreating back until it was stolen from sight by the castle's stonework when he rounded the corner. Automatically, Sherlock's brain launched into action to determine when he was most likely to see John again. They were finished with classes today, which wouldn't resume until Monday, as it was Friday. Sherlock was irregular in his attendance of meals, so most likely not there, especially as he wasn't feeling particularly hungry right now and no desire to force his company on a John who was still unhappy with him. They wouldn't meet face to face at the Quidditch match the next morning and most of John's time after the match was likely to be taken up by the Gryffindor celebration party when they won, which Sherlock knew they would. Even though Gryffindor was playing his own house, Sherlock was unbiased and Ravenclaw had been flattened by Slytherin in their last match. It looked like it would be Sunday morning, when the two of them, perhaps joined by Mary, would normally relax on the grounds when the weather was nice like this. John was sure to have forgiven Sherlock by then; he always did.

Of course, Sherlock realized, if he really wanted to, he could probably meet John at the Owlery tomorrow—John always tried to send an owl to Harry on Saturday afternoons, and Sherlock could easily pretend to have some mail of his own to send.

Vaguely wondering whether or not he could follow through with this plan, but starting to draft a taunting letter to Mycroft all the same, Sherlock started walking in the opposite way John had, thinking of going to the Room of Requirement to read his book. He had just started for the staircases when a better idea struck him, and he quickly looked around the corridors to make sure no one was coming. When he had assured himself he was alone, Sherlock pulled out his long, ebony wand and tapped the crown of his head once, muttering the incantation for a disillusionment charm. It was very advanced magic for a fourth year, and Sherlock knew it wasn't as complete or powerful as one cast by, say, Dumbledore. Nevertheless, it would provide some level of concealment and unless he was uncharacteristically clumsy, it should make it exceedingly unlikely anyone would notice him. Sherlock carefully charmed the library door open, and slipped back inside with even more care.

Sherlock walked briskly over to the Astronomy section, avoiding other students and their gazes as they studied at tables or browsed the shelves. He stopped at what had been his and John's table to check the books John had been using, then continued. At the shelves, he found and slipped a few books on the same subjects into his bag. Later he'd try and plant them in the Gryffindor common room somewhere John was sure to find them, making it look like someone else had been using them and then left them behind, having chosen different books so as not to arouse John's suspicion.

Sherlock checked the rows near him for people, and then made for the exit at the rear of the library. He knew there was smaller chance other students would be that way as he was generally very well versed in where these less-traveled hallways were in the school; Sherlock's knowledge of Hogwarts was a matter of personal pride to him, so he always tried to make sure he kept it updated. As it occurred to him that he rarely went this way himself, he decided to change that.

With his hands in his pockets, the Ravenclaw traipsed down the corridor, looking for anything he didn't already have stored in his mind palace. Since Sherlock had decided to start organizing his memories this way about a year ago it had been gradually growing and developing to become more complex, and knowledge of the castle's layout and secrets was of high priority.

After he turned a corner and walked several more meters, he found something interesting. At first it didn't seem extraordinary, but it caught his attention. It was a closed door. Intriguing, thought Sherlock to himself. Closed doors were unusual at Hogwarts, at least the ones of this variety—normally they would be larger and more elaborate, and located on a wider hallway, not a narrow back one like this. Sherlock turned the handle, but found it locked. "Alohomora," he whispered, pointing his wand at the knob. Locked doors were even more uncommon.

When he pushed open the door to enter, a soft puff of stale air greeted him, ruffling through his fringe and robes. Sherlock blinked a few times, and then walked in slowly, closing the door behind himself.

"Lumos," he said. It didn't look like much, just a disused classroom. He could see flecks of dust swirling through the air languidly from the faint light of a window on the far wall and the stronger light from his wand tip. But before Sherlock could start to wonder why such an unremarkable room was kept locked, he saw it.

Standing straight and grandly by a few stacked desks and chairs by one wall, was a tall, ornate, and ancient mirror. Sherlock approached it curiously, letting his wand tip dim a bit to avoid a glare off the glass when he reached it. It had a carved, stone frame that was etched with patterns and an inscription at the top curving around the somewhat grimy glass. When he looked into the glass, however, he had to step back slightly and blink.

Sherlock had been expecting to see only the empty room, not himself looking back at him, masked as he was by the disillusionment charm, but that wasn't the case—there he was with his tall-for-his-age posture in school robes trimmed with blue for his house and ruffled-up, curly hair, young face pale underneath it, but he wasn't staring back at him, and he wasn't even alone. The Sherlock in the mirror was turned to show his profile, because he was facing another boy and holding both his hands in his. Sherlock glanced over his shoulder briefly to check that he was alone, and then looked back to see that the John in the mirror was really only in the mirror. Then he immediately chastised himself for being so irrational, he'd known he was alone.

Sherlock stared into the mirror, a lone figure barely visible even it you were looking for it, marked by his wand light in a mostly dark and empty room…yet the mirror was anything other than empty. As what he was seeing slowly broke over him, Sherlock let out at tiny gasp. He jerked his eyes back to the top of the mirror, scanning the letters urgently, mind rearranging them, searching for anagrams or other patterns—ah, but of course, it was merely written backwards.

I show not your face but your heart's desire.

Sherlock couldn't help himself, he reached out a hand to touch the glass. There he was, finally having found enough courage to do what he was only now realizing it was his deepest, most desperate desire to do. He was saying to John "I love you." And John wasn't pushing him away, he was pulling him into an embrace.

They were difficult for him in a way nothing else was, so Sherlock had spent years of his life learning to hide and ignore his emotions. John had started to change that, though, and Sherlock couldn't help but think back to the fight they'd just had, about nothing, really. It used to always come so naturally to Sherlock to act like that, disregarding others and oozing arrogance, but knowing John for the past few years had caused the other boy to rub off on him to some extent. Recently, though, Sherlock had been becoming more and more aware of how he acted. But he kept it up because, well…. Sherlock finally admitted to himself that it was because he didn't want John to know. But now he felt like he'd suddenly rounded a corner and walked through a door to come face to face with his heart and all he'd been hiding, both from others and himself, for so long. Now he was being forced to confront this part of himself.

He had been both amazed and relieved in the past few months that John didn't notice how his pulse quickened and pupils dilated around him, how once or twice he'd suddenly smiled just to see him, the way he tried to help him with schoolwork indirectly, that he went to every Gryffindor Quidditch match, but not every one for Ravenclaw, and how even though she was one of the only friends he'd ever had, he found it so hard to be around Mary…how he frequently glanced at John's face when he thought he wasn't looking, his own sometimes looking…sad, because he just couldn't tell him. After all, Sherlock thought to himself, there's a reason the two of us are in our respective houses.

What was this magic? Sherlock stared at the mirror, seemingly unable to blink, to break his gaze and concentration on it for just that moment. A mirror that showed the viewer their most fervent wish? His mind started to brainstorm the different ways such a magical object might work, but then Sherlock stopped himself. He had something far more important to think about.

Until he saw himself do it, Sherlock hadn't realized how much he wanted to, and how much it had been eating at him these past few months not to, especially since John and Mary had started to show interest in each other. Sherlock wanted to tell John that he loved him because it was true. He thought John felt the same way about him, but he had never doubted something so much in his life, perhaps because it was so important to him, perhaps because Mary and whatever John felt for her made everything so much more complicated than it would have had to be already. He had been afraid of losing what they had now.

Sherlock Holmes sat down on the dusty stone floor of the disused classroom to think, slightly detectable for a moment in the shimmer of movement that was the disillusionment charm's flaw. He was just one boy, alone in an empty room that was still full of all his hopes, in a castle full of magic, possibility, and hundreds of other students, more like him in more ways than he had ever stopped to imagine were possible. And one boy, up in a tower in a separate wing, sitting in his dormitory alone and thinking of a friend.

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