A/N: The idea and first paragraph come from Tumblr user doctorwhoatson (as of 2012).
"I couldn't bear the idea of you being dead. For three years, I thought every day would be my last. So many times I stared at my gun, the knife, the rope, the roof...but then I realized how stupid it would be for me to take my own life. So stupid because I knew you were alive. Out there. Somewhere. But you still never came. So, I decided to look for a way to lure you back here. What better way than this? " John Watson smirked, knife in his hand, a pile of dead bodies around his feet. "Welcome back, Sherlock."
Sherlock, for once in his life, was at a loss for words. His mouth opened and closed in quick succession, almost like a fish. He didn't know quite what to say, which was shocking. He almost always had something to say; a deduction, a snide remark, something...but no.
"Sherlock, I knew you would come back," the other man grinned, his eyes wide and crazy. "You came back because you love solving crimes. And you've solved it. You need something se to love. Me. Me, me, me. You can love me now."
"John..." Sherlock finally managed to gasp out.
"Oh, Sherlock," John grinned, stepping closer to his love. Sherlock stepped back subconsciously, his greenish eyes almost struck with fear. "Oh, love, you needn't worry. We will be happy, you and I. You came back for me. Love me."
Sherlock had conflict in him. On one hand, he felt the thrill of solving another unbeatable crime, the Jack the Ripper of the 21st century, but, on the other hand, he knew he had to turn John in, and he didn't want to. John was his best friend, one of he he few people he cared about.
"John," Sherlock said, more firmly, "why?"
"Why? Why? WHY?!" John muttered, screaming the last one. He threw his arms in the air and paced in a circle, looking very much like a macabre ballet, with the blood literally dripping down his arms and face. "Because I bloody love you, you dolt! I. Love. You! And now, you can love me! See? Look at these people! They all stood in the way of our love, and now, they're all dead!"
Sherlock finally did look at all of the bodies, and nearly wanted to be sick. They were all innocent people, people who had done them more good than harm in their whole existences, even if he didn't know them personally. He seemed to float in and out of a stable mind, not knowing what to say. John had done this...John, the army doctor, who had had the occasional bad day, but whom he had never known to hurt anyone in his whole life without reason.
"John. Why? Why?" Sherlock asked, letting his confusion break into his voice. For once, Sherlock's powers of deduction failed him, and he could not deduce what was going on. All that came up was question marks, nothing intelligible or useful. This made no sense whatsoever.
John threw the knife to the ground, the metal making a dull clank against the concrete, and stepped closer, enveloping Sherlock in a tight embrace. He grabbed the back of Sherlock's head and kissed him passionately, moving their lips together. Sherlock pushed him away, a look of disgust on his face as he furiously worked to use his coat collar to rid himself of the blood that now resided on his cheeks and lips. A feeling of nausea overwhelmed him. What was happening to him? Surely, this was all just a horrible nightmare, and he would wake soon...
"See? You love me, too!" John exclaimed joyfully, his face lighting up in crazed glee. "Let's go home, and tell everyone the good news!"
"John..."
Sherlock stared at the knife, and his heart almost sank. Even coated in the blood of the martyrs, he knew what he had to do.
He rushed over at lightning speed and grabbed the knife, lunging on John, who fought back with an element of surprise. He had not been expecting the attack from Sherlock. They struggled for a few moments, rolling around, one on top of he other interchangeably, until the knife fell, and Sherlock accidentally cut himself with it, their rolling pushing it deep within him.
"No...no...this isn't what I wanted. Sherlock! Sherlock!" John screamed, pulling the knife out, the doctoral side of him forgetting that leaving the knife in would has been better. Sherlock, meanwhile, gasped in pain, this not being the outcome he had planned. Pain pinged in his chest where the knife had sheathed itself, blood pulsing from the wound with each telltale beat of his heart. It was almost like a countdown, a countdown to his death. "Oh, God, someone help him! Please! Sherlock!"
And then, his world shuttered itself to blackness.