Disclaimer: I don't own Sherlock, John or any other Conan Doyle or Moffat Gatiss characters. Wish I did.
Collateral damage occurs when something incidental to the intended target is damaged during an attack. When used in conjunction with military operations, it can refer to the incidental destruction of civilian property and non-combatant casualties.
"Sorry, wrong day to die." The Consulting Criminal sounded a bit disappointed.
"Oh, did you get a better offer?" the Consulting Detective asked through slightly gritted teeth.
The retort, "You'll be hearing from me, Sherlock" came echoing off the pool side tiles, and Moriarty departed nonchalantly, calling the snipers off with a click of his fingers, before continuing the conversation on his mobile phone.
This time, Watson took a moment to gather his thoughts before getting to his feet. They had been fooled once before into thinking that Moriarty had departed. Sherlock's laser stare was still fixed on the door through which his nemesis was departing, the browning automatic still firmly gripped in both of his hands. He lowered it only when the dancing red dots on them disappeared, and he could hear the slam of doors from the bleachers above the pool. The snipers were gone.
John came up behind him and said, "well, that's one time I am glad someone left their mobile phone on during a performance." John's voice shook, and was a little wheezy, as the adrenaline took its toll. Sherlock did not reply, just stared down at the tiles, as if lost in thought. Then he suddenly roused himself, pocketed his gun and walked out of the side door, without a word or backwards glance at Watson.
By the time John caught up with him, Sherlock was halfway down the street, talking on his phone to Lestrade. "…and tell the bomb squad to treat the anorak carefully; I don't think that Moriarty would detonate it just for effect at this stage, but it would be wise to take proper precautions." He ended the call without saying goodbye, and John grabbed him by the forearm to stop him from striding off. Sherlock focused his grey green eyes on John's face, with the forensic intensity usually reserved for corpses. "You're bleeding somewhere, I can smell it. Are you alright?"
John shrugged his shoulders. "No, just a bit bruised and bashed. And one of the snipers liked a bit of knife play. But, it's nothing I can't handle with the first aid kit back at Baker Street." Reassured, Sherlock turned away, heading back to the main road.
"Hold on Sherlock, shouldn't we wait around for the Yard team to get here?"
"Hardly, John. This doesn't even qualify as a crime scene as there has been no crime."
"What about the USB stick with the missile defence plans on it? Moriarty may have tossed it in the pool, but it's still top secret. Mycroft will not be amused, by the way."
"Oh, don't be silly, John, I was not about to compromise state security. I told you back at Baker Street that I had returned the real memory stick to Mycroft. What's at the bottom of the pool, and now ruined, was just a plausible imitation, a copy that was good enough to pass rapid scrutiny, but with all the interesting bits altered to make them useless."
"Is that why Moriarty tossed them into the water? He would have figured that you would have done that?" The doctor pulled his thin brown cardigan around him, as the cold on the dark street was starting to get to him. The coat had been left behind, tangled with the bomb vest. "Is it sort of a 'he knows you know, and you know he knows, so both of you play along?"
Sherlock didn't answer, but strode away. John ran to catch up and then fell into step beside him as the pair came to the main road and they started looking for a cab. It was half past midnight, and on a Saturday night, it would be challenging to find one that wasn't already occupied.
After the fourth one passed by with its top light off and passengers in the back, John wondered aloud. "Do you think it's too late to catch the last tube?"
Once again Sherlock did not reply, because he had spotted the welcoming glow of a yellow light coming down the street, and raised his arm. "Taxi!" His deep baritone carried across the distance and the empty cab obligingly pulled up to the pavement. He opened the passenger door and gestured for John to get in, shutting it behind the shorter man. Then the detective leaned in through the half opened front window to instruct the driver. "Take him to 221b Baker Street."
John sat up from where he had sunk back into the comforting seat. "What, Sherlock, aren't you coming with me? We need to talk."
The detective's answer was delivered in a flat tone. "No, I need to walk off the adrenaline; see… you…. later." To stop any protests from John, Sherlock simply said "Drive on" to the cabbie, and walked away.