They both ran, hearts pounding through the dark. Sherlock, the taller of the pair was taking much larger strides and John was falling behind. He could still hear his voice rasping behind him so he knew he was still somewhere behind. He called out.
"John!"
"I'm...here" he shouted back.
The air was dusty and dank. It was cold and Sherlock's breath swirled around him. He thought he might be sick but kept running. He pumped his arms and legs faster, willing an escape to appear. No-one else knew they were here. If they had to get out they had to do it themselves. He darted in between pillars and unidentified objects. He could barely see as his torch flicked light around wildly as his arms swung backwards and forwards.
Sherlock saw a light up ahead. Not from his torch, this light held steady. It was glowing through the gap in between a door and its frame. Relief warmed through him. He launched himself through the dark into the wood. It splintered and the door swung open and blinding sunshine momentarily dazzled him. He put his hand against a moss covered wall and bent double gasping for breath. John tumbled out of the darkness behind and leant against the wall. They looked at each other. John saw something in Sherlock's eyes he hadn't before.
Fear.
Finally John had caught his breath enough to speak.
"What, was that?!" He exclaimed. Sherlock's face told him he didn't know either. Looking back into the dark building they had fled from Sherlock shook his head from side to side slowly.
"It's just not possible" he muttered to himself. "It can't be."
Slowly they both walked away from the building rounding a corner. London reappeared. People bustled past, unaware of the danger to them just a few buildings away.
"I take it we aren't going to tell Lestrade about this" Whispered John, now alert to anyone around them. Again, Sherlock's face said enough.
No.