Author's note: Reveal at the end of the chapter - sort of.

The cab ride to Scotland Yard was uneventful, except for a text that John said Sherlock to inform him that Bill was doing fine, which he showed to Bill's friend while pretending not to see the relief on his face.

"Who is it?" he asked as they walked in the door, not many people around because the sun hadn't risen yet.

He knew John wouldn't need an explanation, and he immediately answered, "Gregson. He is not the most intelligent policeman, but he is the most reliable."

"He lets you use his office?"

"He doesn't have a choice".

No one paid them attention as they walked to the DI's office.

Sherlock had worked with Gregson, but not nearly as often as with Greg. For a good reason – like John had pointed out, he wasn't the best Scotland Yard had to over. He had however the upside of being tenacious as a bulldog once he was put on the right trail. They would never be friend. They never could have been; Gregson was nothing like his DI; and he knew that Greg despised the other man since he'd told the Chief Superintendent after Sherlock's disappearance that he'd always been suspicious of him, even as he called him in on cases. Sherlock didn't blame him. Moriarty's plan had been good, and there had been no reason to expect loyalty from Gregson. He was reliable when it came to catching suspects – so apparently things weren't as different in this universe as they could have been – but not when it concerned his career.

Which didn't mean he didn't harbour a slight resentment towards him.

He might understand his reasons, but he couldn't like him.

But he was ready to admit he had his good sides.

And he – or in this case his office – would have to so. Greg wasn't a police officer here.

He swallowed. He really missed his DI, and the environment only brought to the surface how much. He would have called Greg immediately, if he only had the chance to do so – he would have called him before Mycroft, that was sure.

He couldn't help but wonder if his friend knew how important he had become over the years, important like John and Mrs. Hudson and Molly.

"This way".

Unconsciously, he had walked to the office that would have been Greg's, if this had been the right universe, and he turned around and followed John without an explanation. He could probably deduce why.

Gregson's office was empty, as expected, and John went to his pc immediately.

"He has changed his password, but it won't take long".

It rarely did.

Sherlock looked around.

He hadn't been to Gregson's office often and it looked more or less the same; his desk clean, his walls bare.

Sherlock remembered Greg's office – rather messy, except for his desk, and full of pictures of those he cared for – and felt something he believed others would have described as homesickness. He shook himself. This wouldn't help them. He had to concentrate.

"Ronald Adair" John said, looking for the file, "did you have a similar case?"

"I solved his murder" Sherlock answered simply, and when John turned to him, his eyes enthusiastic, he added, "he was killed by Colonel Moran, the right hand man of Moriarty".

John slumped in the chair and sighed.

"I should have known".

As a matter of fact, he should. It wasn't difficult to deduce. But Sherlock knew why he hadn't, of course – he was still concerned about Bill, like he would be if something similar had happened to John. So he ignored the statement and continued, "He was a croupier who found out one of the patrons of the casino he worked in was cheating. The patron was Colonel Moran. It was how he got most of his legal money after Moriarty died."

He paused and closed his eyes to think. Obviously, Adair hadn't been killed because he had wanted to press charges against Moran; Moriarty – this world's Moriarty, despite knowing better, Sherlock couldn't help but call him by the name he had always associated with the consulting criminal – wasn't dead, therefore he wouldn't need to make money in a legal way.

Had he had anything to do with Adair's death? Jim was not Moriarty, and therefore Moran couldn't be the second most dangerous man in London.

But could he be the first? Could Moran be behind all this? This universe didn't follow any rules, as far as Sherlock could tell. Some people were different, some people were the same, some people were not exactly what they were in their universe, but shared certain characteristics.

Strangely, Sherlock felt confident that it wasn't Moran. He and Moriarty had been – not friends, but they had been useful to one another. And the Colonel had begun his life of crime because of Moriarty.

Moran wouldn't have turned out to be the second most dangerous man in London without Moriarty. He wasn't behind this.

"What are the facts?" Sherlock asked calmly after he'd reached this point. He couldn't go on without data. He had to know what had happened and work his way through it.

"He was shot through his living room window on the third floor. The killer must have fired the shot from the building opposite. The bullet was small, like –"

"It would fit in a pistol" Sherlock finished. "A special airgun. Invited by a gun maker named Van Herder. I have never seen anything like it".

John nodded, processing the information.

"No motive came to light – he was well-liked by his colleagues – he was a croupier here too – and he was apparently so honest that everyone mentioned it to the reporters and they nicknamed him "The Honourable Ronald Adair". I think his death might have been due to the same reason it was in your universe".

It seemed probable. It might be that only the murderer had changed, not the method or motive or victim.

Sherlock walked over and stood behind John.

"Show me everything".

He had never been to Adair's crime scene; he had read about the murder in a cheap motel room and had immediately known it had been Moran, and that he could finally return home. Even afterwards, he hadn't paid much attention to the proceedings, aside from making sure that Moran was locked up for life. He really regretted his negligence now. Maybe a difference could have given him a clue...

Whoever had shot him had been a sniper, there couldn't be a doubt about that.

"When was the crime committed?"

"3 pm".

In broad daylight. So the sniper wasn't exactly like Moran – he had killed Adair at night, when there was no risk that he'd be seen.

Maybe –

"His boss is still alive. This was a hit – the consulting criminal ordered Adair to be killed, and he wanted it to be done in daylight. He wanted to make a statement."

"So we are dealing with someone who is bold and allows no one to interfere" John surmised. "We already knew that."

"True." Sherlock pulled the other chair next to John's and sat down.

There had to be something – something he had overlooked – he refused to believe that he might not find out. He had to. There was no other option.

He was almost despairing when John pointed out, zooming in, "There. In the corner. Is that – "

There was a book lying on the table. It must have been placed there – there was no blood on, but all around it.

The murderer had entered the flat and placed the book on the table for all to see. He – or rather his employer – was more daring than they had given him credit for.

Sherlock knew the book; he had looked through it briefly. It was a story about betrayal and death, and he hadn't thought it interesting.

But he remembered where he'd seen it.

A thought shot through him – something he had ignored until now –

It seemed unbelievable. Naturally it did. He trusted this person; he trusted this person so much that it had never crossed his mind.

At the same time, he finally understood what the relationship between this world and his was based on. It wasn't logic. It wasn't fate.

It was potential.

John had every potential to become a consulting detective, if he had been born like the man who was sitting next to him.

Sherlock could have become Bill.

Greg, if things had turned out differently, would have been a member of his homeless network.

Moriarty, with another life, would have been a friendly man who worked in the IT department at St. Bart's.

There was one person who could have gone wrong; one person who was good and kind and had always looked after him. But if there had been a moment – perhaps in this person's childhood – if kindness had been turned into resentment, and this had later been deepened by certain elements that had stayed the same –

He didn't explain. He simply rushed out of the office, calling out to the other man.

John and Bill were in danger.

Author's note: Did you already guess? And if you did, are you surprised?

I hope you liked it, please review.