Author's note: I want to point out that I know next to nothing about mental illness. Please do not take this as an adequate representation, and please tell me what you're thinking of this story. Reviews would mean a lot to me.

The distress Sherlock felt ran through his mind palace, telling him that he had succeeded. He laughed as he exited the subconscious. Now they were playing.

It was Sherlock's move. No doubt he would attempt to trap him again. Or modify him in some way. He couldn't wait.

Sherlock put the gun away and willed his hands to stop trembling. Of course Moriarty would have taken precautions. Sherlock had taken a long time to realize that there was a consulting criminal in London, and he had been in his mind for years, leaving his cell without him noticing. He was capable of anything.

But so was he. Moriarty had called him ordinary, but he had also realized in the end that they were alike – just enough alike to make Sherlock as dangerous as he had ever been; and he had proven it with those two years during which he had taken care of his web. He had obviously not yet seen what he had done, had not stumbled across the memories. Sherlock wasn't surprised. He had buried them deep. But he would take all the advantage he could get, and being more dangerous than Moriarty thought right now was an advantage.

If he had to unravel his own mind to beat him, so be it. If he turned into a senseless mess who lived in a mental hospital, so be it. But win he must. For his friends. For London.

Sherlock didn't come to see him. He was probably analyzing the whole thing, trying to find a way out. He could wait. He didn't have anything else to do, and he was enjoying the thought that Sherlock had no plan for once. How could he plan for something like this? Jim himself didn't know how he had even found it possible to escape and attack, so how could Sherlock?

He might try to find out when he was bored, but it was unlikely that he ever would be, and it didn't matter why he existed. What mattered was that he did exist and that he could play. And he couldn't get bored. There was too much going on in Sherlock's mind.

It was ironic that Sherlock, after watching him die in the real world, had brought him as close to Heaven as he ever would be.

While Sherlock was moping, he might as well entertain himself, and he strolled off in search of a memory room. Until then, he had not paid much attention to the memories, unless he had watched them out of frustration because he hadn't found access to the subconscious or Sherlock's eyes; it was time to take a more careful look.

He sighed when he saw that he had arrived at yet another happy childhood memory. It was strange for Sherlock to keep so many. Then again, the consulting detective was nothing if not sentimental. Otherwise, he wouldn't keep his pet around.

It suddenly occurred to him, as he was watching Mycroft chase a young Sherlock around, whether he could change his memories. It would be an entertaining exercise, but if he should succeed, he would change Sherlock as well, and he might end up with someone who wasn't fun at all. He would probably try later, but not until they had played for a while.

Sherlock stood up. There was no point staying on the bed and feeling pity for himself if he could do something, and he had research to do. He had only ever learned about mental illnesses as far as he needed to know about them for his work. Moriarty might well just be a delusion created by his mind. If that was the case, there had to be something he could do. He feared taking medicaments that could have side effects, but if it was necessary, he would. He couldn't tell a doctor; as long as there was the chance that Moriarty was truly alive in his mind, as long as it was the best explanation he had and he didn't find a description of a mental illness that explained everything, he would not tell anyone. He didn't like the bargain he had struck, but it was the only way his friends were safe.

He knew his logic wouldn't convince anyone. He knew everyone would think he was insane. In fact, there was a very good chance that he was, but for the certainty he had felt when he had seen Moriarty. He was real. He was guilty of influencing his mind, polluting his mind palace. And Sherlock had to fight him.

He left the flat without telling John. The doctor would have questions when he returned, but for now he needed to be alone with his thoughts, and he needed to go to the library.

Normally, he would have used his smart phone to access the information he needed, but he didn't want his research to be traceable. Least of all he wanted his brother to realize what he was doing and why he was doing it. Once he was in the library and stayed out if the reach of the security cameras, he could claim that he had looked up chemicals or famous criminal cases; no one had to know that he had been collecting information about mental disease.

He raised a hand and a cab stopped in front of him. He told the driver tensely how to get to the nearest library – he didn't want to waste time by him taking a different route – and looked out the window.

London had not changed since yesterday. The city was unaware of the danger that slumbered in its midst.

Moriarty. The man who had been responsible for most that was evil and hidden in their old city, the man who had almost let out dozens of dangerous prisoners, ruined the most important bank of the country and stolen the crown jewels on one day. And he was alive. As alive as he would ever be. It had been foolish to copy him. He must already have been insane before Moriarty had wreaked havoc, or he wouldn't have done it. He should have contented himself with the memories he had of him, instead of shutting him in a cell because he couldn't bear the thought of him, couldn't bear the resemblance between them anymore. It was his entire fault.

And if anything should –

No. He wouldn't allow it. His friends would be safe. The city would be safe. If push came to shove, he would have himself killed. Mycroft might be persuaded to do it. Or order it, at least. But die he would, if it was absolutely necessary.

He arrived at the library and exited the cab, not looking at the driver as he paid him. He had visited it often enough so that he knew how to avoid the cameras – even if he made sure to be caught once or twice so that Mycroft wouldn't think he was evading them. His brother must not get suspicious. He would not stop until he had found out the truth, and Sherlock would end up in a hospital before he knew what was going on. And he had to know before he made a decision. His whole life, he had resented intrusion. He wouldn't allow his brother to put him away or have him killed until he was sure he was making the right decision.

He soon found that most of the books were helplessly inadequate. While case studies were useful in his field of work, he couldn't see how he was supposed to determine whether he was developing an illness through someone else's unique experience. A few books were more academic, however, and offered lists of symptoms he could use.

He worked as fast as he could while still being diligent; he was not going to spend too long at the library, just enough time to safe all the useful information –

He let the book he was reading sink when he realized.

He no longer had a safe place where he could put everything he saw or read. If Moriarty gained access, he might make him think that he was insane, and –

He couldn't worry about that. Too many variables. So he simply kept reading and eliminated all the diseases that didn't fit.

He quickly decided that none did. As far as he could tell, the closest his situation came to was a split personality, but he wouldn't be discussing rules with his other persona in his mind palace in that case. And he should not be able to hide his illness. John should have noticed – long before he had.

After a few hours of research, he came to a conclusion.

He might not be insane. Or, rather, not more insane than he had believed himself to be before he had entered the library. He figured it was good news, but on the other hand, it meant that Moriarty was alive and ready to strike.

And he didn't know if he wasn't already starting the game.