Not 24 hours after Sherrinford, while at his brother's house in Kensington, Sherlock was watching the news. Usually neither brother bothered with such trivialities, but this morning the pair had decided to see if there was anything they'd missed over the last couple of days, while trapped on the island. There were the standard stories about the latest scandal in Westminster, Brexit negotiations, a couple of stabbings here and there, but the one that drew their attention was that of a fire. A fire had spread through an old building that had been made into flats near to Temple tube station. Alarm bells started ringing in Sherlock's mind, he knew that area intimately, and a sense of dread crept over him. His fingers had dialled her number before the news reporter had confirmed it was her building, and after the third attempt with no one picking up the phone on the other end, he leapt to his feet, donned his coat, and shoes, and ran out of the door. Mycroft sighed heavily, made a few phone calls of his own, before following his brother to the site of the fire.
When he got there, he was not surprised to find Sherlock hovering by the police tape, having an animated discussion with Lestrade, and one of the firemen, even his brother was not rash enough to run into a burning building. The cacophony of noise mean that Mycroft had to get quite close to be able to hear what the two were saying, and it did not bode well. The firefighters thought that those who were going to be rescued, or evacuated would have been by now, after spending that long in a smoke infested inferno, there was little chance of anyone else surviving. The first bodies were starting to be brought out, and taken straight to the morgue at St Bart's. He saw Greg and Sherlock share a look at that piece of information, and Sherlock immediately enquired as to who would be carrying out the post-mortems. Lestrade did not want to be the one to tell Sherlock that Raj was on duty this evening, nor that he knew Molly was supposed to be at home. His hesitation received a huff from the consulting detective, who rang the phone in the morgue itself. He hung up after the fourth ring, a hint of auburn hair catching his eye, and before anyone could stop him, he was ducking under the tape, and following the body. Mycroft and Lestrade shared a concerned look, and waited for the inevitable fallout. Not five minutes later, Sherlock swept back past them both, eyes vacant, his body functioning on autopilot. He walked all the way to Bart's, where he sat in numb silence for hours, watching the bodies pour in, and be dealt with systematically.
Eventually he returned to Baker Street, where he sat in his chair, and didn't move for several hours. Mycroft, and Lestrade visited, John came by with Rosie, but nothing could get Sherlock to emerge from his mind. It was like something had broken within him, and he was trapped in his own nightmare. She was still with him there, he could see her, smell her, be with her in everyway she had deserved him to be in life. When he opened his eyes, she was gone, and he was left with concerned eyes, unsure friends, people treading on eggshells around him, avoiding all reference to her, or anything she was involved in.
After a month, he was transported to Sherrinford, and housed in a cell next to his sister, two of the brightest minds of the century reduced to the most nominal of non-verbal communication.