Gunpoint // Johnlock

He tightened his grip on the trigger, pressing his forearm into Watson's collar bone - who desperately gripped onto the metal fence behind him. The sounds of the hectic streets below deafened him, sickening him to the stomach. "One more word, one more pray," the figure spoke, digging the gun into his victims forehead, "and you'll be a dead man."
The click of the safety coming off put his teeth on edge, until he realised who's gun it was coming from.
There stood Sherlock, with his gun also pointing at Watson. Tears were welling in his eyes. "Do you trust me?" He whispered. John was shocked, paralysed. "John, do you trust me?"
Shutting his eyes tight, he gave a reluctant nod.
The gun fired.
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A girl of the age of seventeen was reported missing on the 18th of March. Her last sighting was CCTV footage of Piccadilly station, where she appeared to be running away from something...or someone.
The case seemed too ordinary and mundane for Sherlock, who declined it. That is, until she's knocking at his door, soaking head to toe from pouring rain, begging for a place to hide.