Updated the chapters. Same content, different spacing style. You don't need to re-read if you don't want to.
John was very good at keeping his phone on him and charged whenever he left 221B. He would answer a call or text right away or as soon as he could if he was at work, even if it was Sherlock complaining about how bored he was. So when he didn't arrive home from the surgery and Sherlock texted him three times, he knew something was a bit off. After an hour, he figured maybe John had gone shopping to pick up a few things. After three hours, he figured that John had to stay late and that he was very busy. After six hours he began to worry and after eight, Lestrade had been called and Mycroft had started going over all the security footage. After about fifteen minutes he called Sherlock and told him they had found where John had been taken, an old hotel that was scheduled to be demolished in a few weeks.
He was now in the cab on the way to hotel to find John. His mind was running every detail he knew about the situation and before he knew it he was at the hotel. He ran inside and passed Sally Donovan, headed in the direction of Lestrade's voice. He ran into the room and stopped dead in his tracks at what he saw.
There, in the arms of the DI, was a two-year-old John.
Sherlock wouldn't have believed it was John if it weren't for the big blue eyes and the scarred tissue on the toddlers left shoulder. John looked up, tears running down his plump cheeks, and reached out for Sherlock.
"Sherwock," the toddler cried. Sherlock snapped out of his thoughts and walked over to the DI, taking the small boy from his arms. John buried his face in Sherlock's chest and cried, grabbing the detectives coat. John was wearing his black and white jumper, which was now far to big for him, so Sherlock pulled his coat around John as well. John's cries slowly started to fade as Sherlock swayed slowly and John began to fall asleep.
"What the hell happened?" Sherlock hissed quietly, so as not to wake John.
"I don't know, we managed to take a blood sample and it proved to really be John. He's a little over two years old, we're guessing. As to how he got like this, I have no idea. Whenever the doctors tried to take tests, the poor kid would nearly have a heart attack. The only reason we got a blood sample was because he had fallen asleep for a little bit."
"Who did this?"
"Two older russian men, or so we believe. We found traces of one of their new projects, an age-regressing serum they have at the russian nuclear compound."
John shifted in Sherlock's arms and looked up at the detective, his eyes puffy and tired as his small blonde head poked out of Sherlock's coat.
"Sherwock?" He asked tiredly.
"It's me, John." Sherlock whispered, still swaying. He brought a hand up and rested it gently on the back of John's head, holding it in place while the little one leaned back against him, nuzzling his forehead into Sherlock's neck.
"Does he remember anything?" Sherlock asked once he was sure John was asleep.
"So far you're the only thing he seems to remember." Sherlock nodded and turned to leave.
"I'm bringing him home with me." Before anyone could protest, Sherlock was out the door and in the cab on his way home.
John was held against Sherlock's chest as his hand rubbed John's small back soothingly. He looked down at John and for the first time, realized that he was sucking his thumb. Even Sherlock found it adorable.
Thankfully, Sherlock didn't have any experiments out at the moment so he just had to clean up papers around the flat. When they got back into the flat, Sherlock placed John on the couch and laid his jacket over the toddlers back as a blanket, then collected all the stray papers, putting them in a stack on the edge of the desk. He picked up things on the floor that could be hazardous and moved them out of John's reach.
After the quick tidy-ing was over, he sat down next to John. He was about to go into what John called 'Mind Palace Mode', but just before he swung his legs over the couch he remembered the small toddler residing there. He carefully picked up the small child and placed him on his chest as he steepled his fingers, closed his eyes, and travelled into his mind palace.
Sherlock was pulled out of his mind palace by the screams of a toddler. He snapped out of his trance-like state and looked to the small child on his chest. John was gripping Sherlock's shirt and crying out in fear. Sherlock sat up and cradled him in his arms against his chest, rubbing his back soothingly as he rocked back and forth gently. He pressed his forehead against John's and tried to soothe him.
"Ssh, it's okay, John. It's okay, I'm here. Ssh." The sound of John's sobs broke Sherlock's heart. He'd heard John have nightmares as an adult, and that was painful enough, but as a baby John didn't understand what was going on. He didn't remember the war or getting shot or Sherlock's fall, so seeing it in his sleep was even worse. Sherlock stood up with John still cradled in his arms and held the small child close. He kissed John's forehead and continued to whisper reassurances to his best friend as he brushed John's back with the pads of his fingers. A few moments later, the toddler had calmed once more, and resumed sucking his thumb. He was glad Mrs. Hudson would be out of town for a few days visiting her sister. Sherlock leaned over and picked up his violin and proceeded to John's room. He placed the sleeping John in his bed and tucked him in, then sat on the edge of the bed and began playing his violin, a soft and calming melody to help his John sleep.
This was going to be an interesting experience.