As far as Sherlock was concerned, the day's events proved that he was right to begin with: astronomy was useless.

"It was nothing more than a distraction," he told John, disgusted. "Once I rejected my initial hypothesis, that the position of the planets was significant in itself, the rest was child's play."

The rest of his explanation went well over John's head, but he didn't care much. All that mattered to John was the bottom line, which really was simple. By moving the watch's hands into a certain position, Sherlock opened a secret compartment in the back of the watch. Inside was a tightly-folded scrap of parchment.

The message was short and blunt: Friday. Midnight. Room of Requirement. Come and play, Sherlock. Just you and me.

John stared at his friend.

"Why did he leave a message for you?"

"Obviously, he heard about our investigations," said Sherlock. "He must have recognized that I was the brains of the operation."

"Oy! Remind me who found out about Jim Moriarty!"

"Yes, yes, that was very clever. Remind me to pat you on the back later."

John wanted to go straight to Harry and Ron, but Sherlock insisted on waiting.

"Our evidence is entirely circumstantial at this point," he said. "If we play along with Moriarty's little game, he might reveal more."

"But Ron and Harry could help us. Eight eyes are better than four, right?"

"The message stresses that I must come alone."

For the first time, John really began to doubt Sherlock. Not that he believed Donovan's rubbish theory about him being behind the attacks, of course. But it seemed like Sherlock was more interested in solving the puzzle, as he put it, than in actually seeing the culprit brought to justice. First, he wasted a day decoding the watch while John proved that doing so was unnecessary. Now he wanted to confront Moriarty himself instead of calling in the professionals. John suspected he just couldn't pass up the chance to talk one-on-one with a genuine criminal mastermind.

Once again, they had to compromise. John agreed not to tell anyone about the meeting, on the condition that Sherlock allowed him to come along as backup.

"All right, but stay hidden, and don't come out unless I give you the signal," Sherlock said testily. "He might not show his face if he sees I'm not alone."

"Deal."

The first time John and Sherlock had sneaked out for a little midnight detective work, they had learned a few things, but not nearly enough. The second time had been a complete disaster. John fervently prayed that the third time would be the charm. He was ready for this adventure to be over.

O0O0O

They met a full hour early, just to make sure they got to the Room of Requirement before Moriarty. This was partly so that John would have time to hide, and partly to throw Moriarty off if he was trying to lead Sherlock into a trap.

John had never been in the Room of Requirement before, though he knew its reputation well.

"How do we get in?" he whispered.

"We need a place where I can talk to Moriarty undisturbed," said Sherlock. "We also need a way for you to listen in without Moriarty knowing. Just picture a room like that in your head and copy me."

He began pacing back and forth across a small stretch of corridor, hands clasped behind his back. John mimicked the younger boy, though it made him feel rather silly.

A place where Sherlock can talk with Moriarty, and I can listen in without Moriarty knowing, he thought. So we'll need some sort of screen or—

"Ah!" cried Sherlock. "Here we are!"

John blinked. There was a door to his right that definitely hadn't been there a moment before.

Now, this is a secret passage, he thought as he followed Sherlock into the room.

They found themselves in a cozy little chamber furnished with two armchairs and a fireplace. It looked rather like a miniature version of the Hufflepuff common room, except without all the yellow and black. John had been expecting something grander, but he supposed anything more would be overkill for a meeting between two people.

"Where am I going to hide?" he asked, looking around the room.

"I expect you'll find that mirror opens up," said Sherlock, nodding to a full-length mirror in the corner. "I was envisioning something of the sort."

John pushed gently on the mirror's frame. Sure enough, it swung forward like a door, revealing a room no bigger than a broom cupboard. John stepped inside and pulled the mirror back into position. From this side, he had a perfect view of the larger room.

"Can you see me?" he called.

"No, but I can hear you loud and clear," said Sherlock. "You'll have to be completely still once Moriarty arrives."

The next half hour passed by excruciatingly slowly. John would have been tempted to take a nap if his hiding place had been large enough to lie down in. (Sherlock insisted that he stay behind the mirror, in case Moriarty turned up early.) Sherlock himself showed no sign of drowsiness. He sat bolt upright in his armchair, with his fingers steepled under his chin and his gaze fixed on the hearth. It was almost creepy how little he moved.

At a quarter to midnight, Moriarty arrived.

He looked…like any other twelve-year-old. John felt surprised, then realized that was ridiculous. Evil people would never get away with anything if they looked evil. All the same, he couldn't wrap his head around the idea that this ordinary-looking boy had poisoned three people. His youth alone was disconcerting.

For a split second, Moriarty looked startled to see that Sherlock had gotten to the Room of Requirement first, but only John would ever know that. By the time Sherlock turned his head, the look of surprise had been replaced with a bland smile.

"My, aren't we punctual!" said Moriarty.

Maybe John's perception was colored by what he already knew of the boy, but he thought there was a sinister glint in his eyes.

Sherlock remained completely expressionless.

"James Moriarty," he said.

Moriarty bowed.

"Sherlock Holmes," he said. "I've been wanting to meet you for ages."

"Likewise," said Sherlock. "Though for entirely different reasons, I imagine."

"Oh, I don't know about that." Moriarty took a few steps closer. "You came here to study me, didn't you?"

"To stop you," said Sherlock.

"To study me!" Moriarty repeated sharply. The speed with which he shifted from one emotion to the next was terrifying. "If stopping me was really your primary concern, you would have gone to Saint Potter the minute your little Hufflepuff friend told you my name."

Behind the mirror, John shuddered. It was more than a little disturbing to hear his own thoughts coming out of Moriarty's mouth.

Sherlock stared at Moriarty for a moment before responding.

"You don't give a damn about blood purity," he said. "You didn't even plan for the first victim to be a Muggle-born."

"I would have done, if I'd known what a panic it would cause," Moriarty said, grinning.

"You targeted a Muggle-born the second time, to increase the hysteria."

"Obviously."

"And you're not making any money off of this."

"Not a Knut."

"So it's all just a game," Sherlock concluded. To John's relief, he sounded appropriately disgusted. "This is fun for you."

"And for you," said Moriarty.

Sherlock's expression was unreadable. "You think so?"

"I know so." Moriarty leaned in. "I've been watching you, Sherlock Holmes. Almost since you stepped off the Hogwarts Express. You're brilliant. You're like me. That's how I knew you must be as bored as I was."

There was a long pause. John's heart sank as he realized that Moriarty was right. Sherlock was bored out of his skull most of the time—bored with classes, bored with classmates, bored with life. The only thing John had ever seen him show real interest in was solving the mystery of the poisoned students.

What will he do with himself when Moriarty is behind bars? John wondered.

From the look on Sherlock's face, John knew that he was thinking the same thing. And Moriarty saw it, too.

"What do you want from me?" Sherlock asked quietly.

"Isn't it obvious?" asked Moriarty. "I want you to keep playing the game."

"You want me to join you." Sherlock didn't phrase it as a question.

"If you keep playing the hero, then the game will be over soon. I'll have to kill you." Moriarty said this as matter-of-factly as if he were explaining the rules of Cluedo. "But if you come over to the dark side, we can have fun together for years. Neither of us will ever be bored again. And they'll never catch us, because who else is clever enough?"

In the silence that followed this little speech, John could hear his heart beating.

"Molly Hooper is a friend of mine," Sherlock said at last.

Moriarty threw back his head and laughed.

"Your friend? You're Sherlock Holmes! You don't have friends. You have enemies and pets." He adopted a posh accent that was a perfect parody of Sherlock's. "Fetch, Molly! Good dog, Molly. And good dog, John, getting me that name. Remind me to pet you later!"

Moriarty shook his head. "A man can't be friends with a mutt, Sherlock. The only person in this school—in this world—who could really be your friend is me. So what do you say?"

He held out his hand. Sherlock stared at it for a moment, then shifted his gaze to Moriarty's face.

"Two words," he said. "Vatican cameos."

John was out from behind the mirror in a flash, his wand pointed directly at Moriarty's heart.

"STUPIFY!" he screamed.

John was an exceptional dueler. He didn't have Sherlock's encyclopedic knowledge of spells, but he had great aim and concentration. Most importantly, he was fast.

Moriarty was faster.

Afterward, John was never sure what exactly had happened. One moment he was bursting out of hiding, and the next he was lying on the floor.

"John! JOHN!"

Sherlock's face appeared above him, looking even paler than usual. In his dazed state, it took John a while to realize that he was seeing something new: Sherlock afraid.

"You had your chance, Sherlock." Moriarty's voice came from somewhere in the distance. "Now I'll have to destroy you."

He paused.

"And your little dog, too."