I'm sorry, this 221B is one of those that I just couldn't ignore - as much as I have other things to write (yes yes! I'll write that tonight - okay?)
Apologies for the content and feels.

There are seventeen stairs from flat 221B to the small hallway that led to the front door.

Seventeen stairs; and John knew every one of them…. intimately you might say.

Over the two years he had lived in the Baker Street flat he had chased down them (and back up again), sat and laughed on them, and more recently cried on them, but today was only the second time he had been led down them in handcuffs.

The last time he had chinned the Chief Superintendent. Sherlock had looked at him and smiled.

This time though was worse; much, much worse.

Mycroft had betrayed his brother. He had given him up, sacrificed him on the altar of State, and handed Sherlock's life to Moriarty on a plate. It was he, as much as the Consulting Criminal that had destroyed a life still filled with such potential.

Potential that will now never see the light of day.

And John felt that he had failed in his self-appointed task of looking after Sherlock, of watching his back and keeping him safe, so he did the one thing that to him made the most sense.

Lestrade looked devastated as he read him his rights. John just smiled.

If they find enough bits of Mycroft to bury, they could put him next to his brother.