So this just popped into my mind and I wrote it in about 20 minutes so I'm sorry if it's not as good as you had hoped. The lovely beginnings of some Johnlock :)

Fear wasn't an emotion Sherlock felt often. He could remember very clearly the last time he felt true fear, though he didn't like to think about it. It was a long time ago, long before he met John. But, of course, almost all of his emotions had been odd since John had arrived, so the feeling of fear shouldn't have been too out of place.

But it was. The moment he ran back into the room yelling, "John! I've got it! The cipher, the book…" he stopped dead when he saw the symbols spray painted around the flat. He hadn't been gone that long, it was impossible. Fear gripped him so tight, for a moment he couldn't breathe. "John!" he yelled, not hearing a response. The book fell from his hands, and he turned to dash out the door. It was the first move he had made in years without thinking it through, calculating his every step before so much as moving a muscle. But this was John, and John was impulse. He had entered Sherlock's life, become his flatmate on an impulse, and as they grew closer, Sherlock felt like a large portion of his movements had become more impulse than thought, at least when John was involved. Something about the man changed him.

Realizing he was no good running into a situation blind, Sherlock managed to calm himself, forced himself to stop and think. He knew where they were, if he was correct. Of course he was correct. He was rarely wrong. But he couldn't go barging in without a plan. He needed a plan, this involved John, he couldn't act on impulse. Couldn't risk losing his blogger. The thoughts and emotions racing through him would have to be fully examined later, but now he had to get John out safe.

He had a plan, he honestly did, but once he was there, once he saw John and the girl, Sarah was it, tied up, his plan was gone. His mind was nothing but 'John. Save John.'

The change of emotion John was bringing about could explain why, after untying Sarah, Sherlock tried to soothe her. Normally, he wouldn't care about a victims feelings, but this was different. John cared about her. And Sherlock cared about John. So, he touched the near hysterical woman's shoulders and told her, "It's okay, it's over now." He flicked his eyes up to meet John's, and saw wonder and thankfulness there. He gave the doctor a curt nod, and stood up to let John take over calming her down.

After talking with Lestrade, which John did most of, Sherlock had retreated into himself, John told Sherlock that he would be taking Sarah home and would meet him at the flat later. Sherlock gave him another curt nod and went to hail a taxi. Hopefully, this would give him time to at least partially process the reason behind the death grip of fear that had come with the realization that John had been taken.

But, when John walked through the door a few hours later, Sherlock still felt confused. John sat in his chair next to the couch and took the sight of Sherlock in. "Thank you."

"For?" Sherlock didn't look at John, he continued staring straight ahead.

"Tonight. Saving us."

Now, Sherlock turned and locked eyes with John. "I'd be lost without my blogger."

For a moment, neither of them spoke aloud. Their eyes, however, spoke volumes. The confusion Sherlock would never admit to was evident in his gaze, and the reassurances John would never speak aloud filled his eyes. Sherlock stood up abruptly, walked over to John, and waited for the man to stand up. He wound his long arms around John, pulling him into one of the most awkward hugs of all time, because it had been years since Sherlock Holmes had voluntarily hugged someone besides Mrs. Hudson. John didn't mind, though. He snaked his arms around the tiny but tall frame that was his best friend, and squeezed gently. They stood like this for a while, John's head on Sherlock's chest, Sherlock resting his chin in John's hair. John was the one to pull away first. He stretched and yawned. "I'm going to try and get some sleep. You should to."

Sherlock nodded. He gave John a small smile before flopping back onto the couch. John sighed in a way that said, 'I can never win with you' and turned to head to his room. Sherlock watched him go, feeling a bit more settled with his emotions than he had in a while. Having John around was wonderful, even if he did bring all sorts of emotions Sherlock was sure he had buried, because, after all, emotions do nothing but get in the way. Right? He wasn't too sure about this anymore. But a deep feeling of contentment had spread through him when John had squeezed him in the hug, and it hadn't fully left. He sighed and let himself wander back into his mind palace. He may have deleted the solar system, but John was one thing he could never dream of deleting.