This is set during The Great Game when Sherlock goes to confront Moriarty for the first time.

Sherlock paid the cabbie before getting out of the cab, watching as he drove away before picking the locks, and going into the pool, slowly looking around. He was, for once, anxious. In a way, that added to the excitement.

“Brought you a little getting to know you present…” Sherlock said, cautiously looking around. “Oh, that’s what this has all been for, isn’t it? All your little puzzles, making me dance. All to distract me from this.”

The door opened, and Sherlock watched as the person stepped out into his view. He paused, his hand in the air with the USB disk in it, looking around at the person. This Moriarty who had him playing his game.

But then he saw who it was. John Watson. Sherlock looked him over once. He was older than Sherlock, shorter, but far kinder than Sherlock could ever be. In the past few months of knowing each other, John had taught Sherlock far more about people than he’d ever known before. Also, seeing him now before making any deductions, Sherlock learned that even he could be fooled. Mycroft had always told him caring was a disadvantage, and John Watson was the proof of that... Sherlock scolded himself as he felt his heart sink, and an overwhelming wave of sorrow and hurt washed over him. And then John spoke.

“Evening.” John said, voice emotionless, “Well, this is a turn up, isn’t it, Sherlock?”

“John,” Sherlock whispered, “What the hell –”

“Bet you never saw this coming.”

Sherlock’s mouth fell open, and he could hear his heart thudding rapidly. He somehow managed to push himself forward, but stopped when John pulled his coat back, showing Sherlock the wires of a bomb which could blow John’s brains out in an instant, and undoubtedly Sherlock’s too. Oh God, oh God, oh God…

“What… would you like me to make him say next?” Beams appear over John’s body. Of course there’d be snipers waiting… “Gottle o’ Geer, Gottle o’ Geer, Gottle o’ Geer…”

“Stop it!” Sherlock hissed. This was too much, but he knew he had to be strong. John himself was trying not to whimper. He saw the look in Sherlock’s eyes when he saw him, and he knew Sherlock thought he was the scumbag killer Moriarty. That’s what Moriarty wanted him to think.

“Nice touch this, the pool,” John continued reciting the words as they flowed through the earpiece he’d had thrust upon him. “Where little Carl died. I stopped him-” John paused, inhaling a shuddering breath, “And I can stop John Watson too. Stop his heart.” His voice broke on the last word, and both he and Sherlock, unknowingly, felt a tweak at their hearts simultaneously.

What happened next surprised them both. The gay bloke Molly Hooper was dating, Jim, came into the pool. Sherlock could see the crazed look in his eyes. This could be it. They could both die, and Sherlock knew it. Moriarty had already killed an elderly woman and innocent others, for crying out loud.

Words were exchanged, but Sherlock was in auto-pilot. He didn’t know what he was saying. He just couldn’t let John die. It was the only selfless moment he could remember. He just didn’t know John couldn’t let him die either. Not when he’d finally found a real friend. John would be nothing without Sherlock. He knew this, and it scared him.

'Can we expect a happy announcement by the end of the week?’ Mycroft’s words ran through John’s mind for a moment, and in a shocking moment of realisation, he realised he wouldn’t mind that at all. He looked at Sherlock, his gorgeous best friend. Even before he realised his feelings for Sherlock, when he was still one hundred and ten percent straight, he had mused to himself over Sherlock’s beauty, with his bouncy curls and long, beautiful, pale face, and long slender body. And even though Sherlock drove him absolutely bleeding mad, here they were, the two of them against the rest of the world, against a criminal mastermind, and the idea that Sherlock could even possibly be hurt made him furious.

John picked a moment and took it, grabbing the Irish man in a headlock. “Sherlock, run!”

“Oh, good, very good!” Moriarty giggled. He really was insane, but even he had a slight worry, old Johnny-Boy really was loyal, he might just do it. He really might just sacrifice his own life for Sherlock.

“Just like that,” John said through gritted teeth, “Pull that trigger, Mr. Moriarty, and we both go up.”

“He's sweet, I can see why you like having him around,” Moriarty said to Sherlock. “But then people do get so sentimental about their pets. They're so touching and loyal. But oops! You've rather shown your hand there, Dr. Watson. Gotcha!”

Lasers appeared on Sherlock instead, and he dropped his hands to his side.

After a few threats and what not, Moriarty excused himself, and walked off. “Ciao, Sherlock Holmes.”

“Catch… You… Later,” Sherlock replied slowly.

“No you won’t!” Moriarty called over his shoulder.

Sherlock hastily got the jacket and bomb off of John and slid it along the ground, before thanking John for… you know… That thing that you did.

And then, the lasers reappeared.

“SORRY BOYS, I’M SOOOO CHANGEABLE! It is a weakness with me. But to be fair to myself, it is my only weakness. You can't be allowed to continue. You just can't. I would try to convince you. Everything I have to say has already crossed your mind.”

And then everything went black.

 *******

Sherlock woke up in a white room. The smell of lilies invaded his nose and he scowled. But the scowl was because Mycroft stood over him, peering down at his younger brother. Mycroft was nervous about what Sherlock would ask. He’d be beyond devastated, but he’d already had Sherlock’s flat de-drugged, and made sure there was really nothing of risk. When he was able to leave, Mycroft would stay with him at his flat, and he and Mrs. Hudson would keep a close eye on Sherlock to make sure he didn’t do anything drastic.

He could hear an obnoxious ringing in his ears, and came to his own conclusion. “The bomb went off then?”

Mycroft merely nodded.

“John. Is he alive?”

Mycroft sucked in his breath. Here goes nothing. “He wasn’t as lucky as you. He didn’t fall in the pool… Sherlock… They’re not sure he’ll make it.”

Mycroft watched as Sherlock closed his eyes, his hand flicking out to lower the amount of morphine he was receiving. Mycroft knew that was a bad idea; Sherlock would have one hell of a migraine, but he didn’t stop him from doing it. He supposed it was to counteract the pain he felt physically and mentally.

“Please,” Sherlock whispered hoarsely, “Leave.”

“Sherlock I –”

“Mycroft,” Sherlock snapped. “I just want to be alone.”

Mycroft nodded and left the room. On his way out, he saw the doctors and nurses running into John’s room. That was it. John H. Watson, Mycroft’s little brother’s best friend and first love, was dead.

Even Mycroft felt mournful. John was a brilliant man, very good for Sherlock. He kept him right, and with John’s help – and probably more owed to his sass – Sherlock had stayed away from drugs. Now, however, Mycroft could sense a relapse coming along.

*******

“I’m terribly sorry, Mr. Holmes. Mr. Watson didn’t make it. There were complications during his surgery. There’s nothing we could do.” ‘Except not mess up in the first place,’ Sherlock thought bitterly. Perhaps he even said it aloud.

Sherlock stared up at the solemn-faced doctor, and felt the tears travel down his face. He didn’t care anymore. He just nodded, and watched as the doctor left the room. When the coast was clear, he yanked all the medical equipment off of his body, pulling himself to his feet. He opened the window, and looked down. It wasn’t too far down.

He jumped out the window and landed on his feet, stopping to allow the ground-shock to fade away. Everything hurt, and the ringing in his ears was driving him bonkers. Clutching the back of his hospital gown, so other’s wouldn’t see a sight they’d never forget, Sherlock hailed a taxi and got inside.

“221b Baker street,” he told the cabbie, and was off immediately.

When they arrived, the cabbie looked at Sherlock. It was then that Sherlock realised he didn’t have his wallet or any money on him. He instead slipped off his Rolex watch. “Here. Have this instead. I don’t need it anymore, anyway.”

He was out the door before the cabbie could state his gratitude. With shaking fingers, Sherlock unlocked the door to his and John’s flat. Running up the stairs, he couldn’t help but reminisce about all the moments he and John had shared. My John, he thought to himself.

Pulling the flat apart, Sherlock found with a bitter frustration, that Mycroft had had the flat raided and ensured no drugs were around. Sherlock flew into John’s room, and didn’t allow himself to pause to break down. John’s room was obviously left untouched, probably a respect thing, and he pulled open the bedside drawers beside John’s bed.

Snugly tucked under a book and John’s laptop was his gun. The one John had used to save Sherlock’s life after the incident with the cabbie. A Study in Pink, John had titled it. Right before he pulled the trigger, Sherlock spared himself one more thought. ‘Caring is definitely not an advantage.’