Is Sentiment a Chemical Defect?

Chapter 1

Months after Moriarty's 'Did you miss me?' stunt brought Sherlock back to England, the world's only consulting detective was in a purple shirt and trousers, despite the humid July weather, playing a lullaby on the violin.
"Did you like that, Hamish?" Sherlock asked when the song ended, "Ok, now I am going to play you a song that I composed during what your father's blog called "A Scandal in Belgravia". It is about a woman, or rather The Woman."
As the meaningfully strung notes floated through 221B Baker Street, John and Mary were enjoying their first night off since Hamish's birth; at The Landmark Hotel London, the very restaurant where John had originally tried to propose, and where Sherlock had told John that he was still alive.
Interrupting the song, Sherlock's phone bleeped. It was Mycroft.
"Oh, how delightful." Sherlock murmured as he read the text.
'Sherlock, further government investigations have been made into Moriarty's media hack a few months ago. I am afraid that the route you were following is a dead-end. Back to the drawing boards, brother dear.'

Sherlock hastily put his phone down onto his overflowing desk. He turned on his heels and walked towards the wall with the sprayed on smiley face. In an unnervingly calm manner, he unpinned the boards, notes and photographs that he had positioned to organise his thoughts on Moriarty's return via Great Britain's screens. Rather than finding a bin, he simply dropped each item once it was un-attached and left them piled on his sofa.
"It seems all that work was a waste of time," he remarked to Hamish, cheerfully, "I'll just start from the beginning shall I?"
Again the tune of The Woman circled Hamish's carry-cot and weaved in and out of the clutter in the flat; but the notes were tense this time and somehow rough and sharp. Before the sixteenth bar, Sherlock dropped his violin and bow onto John's old armchair.
"Sorry Hamish, I just need some... you know... things," he said cautiously remembering John's strict instructions not to mention anything un-sanitary in front of Hamish. Sherlock suspected this included cigarettes.
His first idea was the skull, which he found was missing; most likely, he thought, because it might 'scare the baby'. Although Sherlock was very fond of Hamish, he hated all the alterations he had to make because of him, alterations to his home, his actions,his behaviour. Next in his quest for smoke was the fridge; thenn the fireplace grate; then behind the radiator; then inside the boiler. John had taken his entire stash.
Sherlock promptly gave Hamish to Mrs Hudson and headed out of Baker Street, having persuaded himself that cigarettes were a better idea whilst babysitting that shooting the wall or harder drugs of any kind.

***

"Traces of calcium carbonate and, what's that? Lead?" Sherlock said to Hamish, as he was the only other person in the room, "Where has he been in the past two days that he could have got both substances on his shoes?"
A few microscope dial turns later and during one of Sherlock's musings, John and Mary arrived at 221B.
"Sherlock!" John exclaimed, "Are you using Hamish as a replacement for the skull?"
"Relax," Sherlock said with the nonchalance definitely absent the evening before, "He's doing fine."
"Where are you off to?" asked Mary, picking up Hamish and kissing him on the forehead.
"Scotland Yard: I have some information for Lestrade; it's about the Mayfair case."
"Oh, is that the one with the extra set of footprints?"
"Yes. It's quite interesting actually; the blood making the second trail is different from the first, but exactly the same shoes. Why would the killer return, surely he would fear getting caught? Anyway, it's around now that I gather ordinary people finish work so I should go. Goodbye Hamish."
He wrapped the familiar blue scarf around his neck and turned up his coat collar, as always before departing.

***
Marching with intent through the offices of Scotland Yard, Sherlock looked straight ahead towards the end of the corridor. He always made an effort to avoid eye-contact with anyone who worked there. It was not so much that he wanted to express his intellectual superiority by not acknowledging them, but more to do with the cold looks he usually received. They all needed him there. Only Lestrade wanted him there.
"Oh." Sherlock said after entering Lestrade's office containing quite a few people but not Lestrade, "Where's Lestrade?"
"He's gone – got sacked," retorted Donovan, "because of you." Her eyes glanced towards the chief inspector and then back to Sherlock. "You got too involved in his cases and the head of Scotland Yard didn't fancy an amateur detective poking his nose into the police's business which, after all, is supposed to be inclusive to the police. So whatever you had to say to Lestrade, don't and don't try to interfere with us again or, well we'll have to make you. Ok with that, freak?"
Without another word Sherlock turned around and left the office.

As he left the premises, Sherlock searched his mind palace trying to think of the last time he actually saw Lestrade: he had been working alone on the Mayfair for weeks, maybe more. Soon, he found it: 39 days ago. Judging by the fact that clearly no one else was occupying his office and several details that only Sherlock would see as relevant such as the marks on the bottom of the door and visible content of the bin, Lestrade had only recently lost his job in the past few days, a week at the most.
Sherlock had been helping him with his cases for years. Why was his input suddenly so undesirable that Lestrade was deemed incompetent by association? And why had Sherlock not found out straight away?

He decided not to get a cab home and instead walked slowly through the mazes of alleyways back to 221B. It was a dark and clear night, at atmosphere that one cannot help but become thoughtful when encountering it, Sherlock was no exception. He found himself longing for the days of solitude before he had met Lestrade, Molly even John. Life was so much simpler back then: just cases to solve; no friends to keep happy, no need for sympathy, manners, or careful behaviour. Mycroft was right, he had changed. He'd softened.

Sentiment is a chemical defect found on the losing side.