221B BAKER STREET
When John and Mary Watson walked into their friend's flat, they found Sherlock sitting in his chair, eyes closed, legs crossed, palms pressed together and resting under his chin. The world's only Consulting Detective was clearly deep in his Mind Palace.
Sitting precariously on the armrest on Sherlock's right was a small, hard-covered notebook that looked like it had seen better days.
When the detective still hadn't acknowledged their presence after five minutes John demanded, "Well, I'm assuming its important. Or else you wouldn't have summoned us here early on a Saturday morning?"
Sherlock's eyes snapped open.
Not bothering to greet the couple, he instead indicated the notebook with the tilt of his head. "What do you make of it?"
John walked over and picked it up, turning it over in his hands, looking at the front and back covers before handing it back. Shaking his head he replied. "It's a notebook… a beaten up old notebook. What of it?"
"It was left lying against the front door this morning in an unmarked envelope," Sherlock explained.
"No note?"
"None."
"What's inside the notebook?" Mary asked.
Sherlock smiled approvingly at her. Getting up, the book still in his hand he replied. "Inside this innocuous looking battered notebook, its contents includes though not limited to, instructions on how to incapacitate, maim and kill someone. "
Understanding flickered across Mary's face. "An assassin's handbook."
Sherlock nodded.
"Do you know whose it is?"
Sherlock walked over to the former assassin, opened the notebook so she could read the inscription on the inside cover.
A.G.R.A.
"Yours."