Slight change of POV in this chapter, just because I felt it was needed.

Sherlock turned to face his brother as the other man walked into the room. He watched as Mycroft sniffed at the air before looking at the puzzle on the floor, as if there was no one else in the living room alongside it.

'I see,' he said as he moved closer, never taking his eyes off the interconnected pieces. 'Any ideas?'

'A few,' admitted Sherlock, 'but I wanted to let you have a look before I said anything.'

Mycroft went to stoop down for a closer inspection, but stopped after a moment's consideration.

'How's the diet going?' teased the younger of the two brothers.

'My diet is going fine, Sherlock,' came the sighed reply. 'How is our dear friend Jim?'

'Jim?' asked Sherlock, acting innocent.

Mycroft threw his brother a look. 'Jim Moriarty. He was here last night, and this morning. Did you really think you could hide it from me, brother?'

Sherlock looked down. 'How did you know?'

'There's a smell of cologne in the air, but it isn't overbearing so I would assume it's had time to diffuse and mellow, meaning it's been here for a while. There's an empty cup of tea by John's chair, but I know he's with Mary and hasn't been back here in the past two days since I gave you the case. Also, his chair looks recently sat on, due to the depression in the centre where the gravity pressing down has been increased. But again, he hasn't been here. Your clients don't sit on John's chair, and there are very few people who would come and visit you if not for assistance-'

'You included,' said Sherlock snidely.

'Business is business, brother mine,' replied Mycroft as he looked around. 'The bedroom?'

'He's not doing any harm, Mycroft.'

'I don't want him compromising the case, Sherlock.'

'He won't,' replied the younger defensively, standing so he was at full height but still just shorter than his brother.

After studying him gravely, Mycroft backed away. 'He had better not.' He turned back to the puzzle. 'What have you deduced?'

'The missing diamonds are fake. They were stolen, by a "good Samaritan" of sorts, I suppose, to bring the people's attention to it.'

'And how did you figure that out?'

'Is it not obvious, brother?' Sherlock asked incredulously. 'The picture is of a stained-glass image of a diamond. Stained glass, Mycroft. A diamond envisaged in glass, surely a sign that the missing ones are fake. And also, look at this corner,' he said, pointing it out to his brother.

'What is it?'

'A signature; "Rev46",' he replied as he went to open John's laptop. He logged on – John's password was so very obvious – and Googled the signature. 'A quick internet search for said term brings up nothing but physics revision pages, which doesn't quite come into correlation with our discovery. Obviously not that then. So what could it be? Separate the "Rev" from the "46" and you get directions.'

'The Book of Revelations, chapter four, verse six,' thought Mycroft.

'Exactly,' cried Sherlock as he went to his bookcase and pulled out an old, leather-bound bible. '"Before the throne, there was a sea of glass, like crystal. And in the midst of the throne", et cetera, ad nauseum, you get the point. "A sea of glass, like crystal?" These missing diamonds aren't diamonds at all, they're cheap, silicon dioxide knockoffs.'

'Very well done, brother,' replied Mycroft, face neutral. 'I shall inform the South African government, see if we can't aid in the recovery of the real treasures.'

Sherlock watched as his brother turned to leave, intending on going to see Jim. He was halted by his name being called from the door.

'Oh, and Sherlock?'

'What is it, Mycroft?'

'Do be careful,' said the elder brother lowly. 'Caring is not an advantage, especially not when it concerns someone like him.'

'I know, I know, you've said it all before,' replied the shorter. 'Now go, get out. I have things to be doing.'

With one last meaningful look at his brother, Mycroft Holmes left the room, and Sherlock listened out for his footsteps all the way down the stairs and out of the vicinity, not moving until the sound of the door to the apartment echoed through the rooms and hallways. Then, he went back to his bedroom, where Jim had been, and hopefully still was.

The full quote from Revelations 4:6 is:
'Before the throne there was a sea of glass, like crystal.
And in the midst of the throne, and around the throne, were four living creatures full of eyes in front and in back.' (from the King John's Bible)

It took me a while to think of an idea, so I hope you liked it. I'm pretty proud of it, so there.