The Bravery of the Soldier
The first time Mycroft Holmes saw John Watson he had to admit that he wasn't as disgusted by the army doctor as he was by some of his brother's pet projects. Mycroft still didn't expect John Watson to last long. Sherlock grew bored easily. It was only ever the truly interesting cases that held his interest for long. It was one of the few times Mycroft Holmes had been wrong.
How embarrassing.
So he did his research and arranged a meeting. It was frustrating that Doctor Watson refused to spy on Sherlock for him, but far from disastrous. He had other, far more reliable methods of observing his little brother than Watson, who was no doubt subject to all the usual human failings. No, the offer was primarily to get a further grasp of John Watson's character. At first, his refusal only lowered Mycroft's opinion of him. Later, it raised him to the highest esteem.
"This is a matter of the highest security, and therefore of trust."
"You don't trust your own Secret Service?"
"Naturally not. They all spy on people for money."
Unlike you.
It went unsaid. The reason John Watson was trusted. Or one of the reasons. The other being Sherlock, of course.
But that was later. Earlier he merely considered John Watson to be Sherlock's project. An 'Honourable Man'. Though John had proved himself to be one of those rare specimens where the title 'An Honourable Man' was bestowed rightfully, Mycroft did not consider that a compliment.
Not surprising really.
Mycroft lived in a world in a world where lies, manipulation and power plays were a way of life. A way of, ironically, doing the right thing. Many would consider it corrupt, unjust, unfair and wrong. Not least that one man, virtually unknown to the British public, could have so much power. If only they knew how much it was for their own good.
Mycroft had assumed that Watson would be of that predictable bent. But Doctor Watson despite all evidence did not view the world with an annoying black and white morality as he had originally suspected. But although The Man had taken an immediate dislike to him, he supposed not unduly, he had kidnapped and threatened him after all, Watson seemed to accept Mycroft as necessary in time. They even formed a bond, of sorts, over the protection of Sherlock, but that came much later.
Mycroft found in those early days that Watson could twist and turn, he could kill a man to save a life, Sherlock's life, even without being ordered to do so (good soldier that he was), technically breaking the law.
But even after that single shot was fired Watson was still suspect: who knew his motives? It could easily have been the rush of adrenaline that he craved that caused him to fire that shot that night. Who was to say that when the rush wore off, that when he realised what this new life with Sherlock entailed he wouldn't back off, leave, choose the 'honourable' 'right' 'legal' route.
But he didn't. He stayed.
And for the first time he had to admit that Sherlock had judged a man's character better than he had, for though he had always been as cold as Sherlock, he had always understood emotions better than Sherlock. Mycroft had been convinced that this honourable man would leave, but Sherlock had known, from the moment they had met that he had what John Watson needed, and that John Watson would stay because of it. That Watson would take the flat, despite the mess, would accept this strange, half mad man.
And perhaps Sherlock had even known that John Watson had what he needed. Or perhaps neither of them did, at that time. But the knowledge, conscious or subconscious, was there.
Perhaps he was getting sentimental.
And so that was why Doctor John Watson, Captain John Watson, was trusted. Always.