It happened in the middle of the case.
It wasn't a very complex case. Shouldn't have caused any problems. Sherlock was walking with John, closer than they had in the past. The silence was comfortable; they were comfortable for the first time in a long time.
They were scouting around an area that their suspect had been known to frequent, when the suspect himself showed up. The man was tall, well-built, track marks on his arms. He was desperate for a fix, and, God, if Sherlock didn't know what it was like to feel that way. Knowing Lestrade was nearby, Sherlock began to speak, telling the man in a calm tone that he ought to stay where he was, that he knew he had to feel like hell, and that matters would be sorted out shortly.
Then the man removed a gun.
For a split second, Sherlock was stunned. He felt sick, body tense. No longer was in London: he was in Serbia, on the rooftop, in every place that had ended in violence and made him feel helpless. Everything was spinning, spinning, spinning around him, and all he could think was, I can't let him kill John. The suspect removed the safety, and Sherlock sprang into motion, trying to pin the man. They were a tangle of limbs, and the man shouted.
There was a gunshot.
Sherlock's leg felt as if it was on fire. Jaw clenched, head swimming, he stayed on top of the man until John forced him off, all but dragging him away. John, too, held a gun, and aimed it at the suspect's head until Lestrade and his crew arrived.
Lestrade cuffed the man and took the suspect's gun with gloved hands, safely unloading the gun. "Christ, Sherlock."
"It's fine. It-it was just a graze." Sherlock let John force him into an ambulance. He wasn't sure when one had been called. "I don't need to go to the hospital, I'm-"
"Shut the hell up," John said. His voice was low, face pale. "You're going to the damned hospital and getting stitches."
Sherlock stared at John, gaze flickering over his form. There was blood on him, but only from Sherlock's leg. For once, Sherlock didn't argue.
John was sullen throughout the entire process, watching as Sherlock was treated at the hospital. It was more than a graze, but it was just a flesh injury, no bones broken. It only required antibiotics, stitches, gauze, and painkillers. Several times, Sherlock asked if he was all right, though each time he was met with short response of "I'm fine," or, "Don't worry about it."
He'd hoped the painkillers would stop the frantic thoughts. They weren't strong enough to do that, though. Instead, Sherlock found that he couldn't focus on anything anyone was saying, a little drowsy. John spoke to him several times. He looked like he was saying something important. Sherlock could only stare at him with glassy eyes.
By the time they were home, they were both spiraling. Sherlock wasn't entirely lucid, but he was panicked still. I could have died. How are you protecting anyone? How can you protect anyone? asked John in his mind. Sherlock didn't know. He didn't know.
"I'm sorry," said Sherlock, curled up on the sofa next to John. His head was resting against John's chest, injured leg extended towards the opposite end of the sofa. It was as if any progress made by medication or therapy had dissolved in that moment into nothingness, leaving him with the heavy feeling of guilt once again. "I'm sorry that...we were in that position. I meant to help you. I'm sorry. I'm supposed to protect you. I'm sorry."
"Sherlock," John whispered, voice strained. "please stop apologising." He rubbed his jaw with his hand, clearing his throat. "Don't you remember what I said at the hospital? Or were you too excited about everything?"
John's heart was pounding. Sherlock looked up. "I didn't...I don't remember. I'm-"
"I swear, if you apologise..." John didn't finish his sentence. Instead, he exhaled sharply.
"John?"
"I told you that I'm the one who shot you by mistake." John licked his lips, hands in fists. "I meant to shoot him, just in the leg, but you moved so fucking fast. I've never shot someone who didn't deserve it before, Sherlock. And now we have to deal with all of this."
Sherlock watched the way the light from a car outside washed over John's face. There wasn't much colour in his face, and his breaths were short and sharp. Sherlock rested against his chest again. His heart was still pounding. "It doesn't matter."
"I shot you. Of course it bloody matters."
Hell if he knew what to do. John's going to leave. Sherlock looked up at John before sitting upright, body swaying lightly. He leaned forward and pressed a kiss on his cheek. "We're okay." He didn't care if it was a lie.
Sherlock rested next to John, eventually falling asleep. John pulled a blanket over them both so they could rest, though, they each woke the other up with nightmares throughout the night.
John sat down with Sherlock the next morning while they each sipped at their coffee. Neither had slept well, though Sherlock was lucid. Very little was said between the two of them. Sherlock felt tense, sneaking glances at the other as he read the morning's paper, skimming the obituaries to see if there were any interesting deaths.
Finally, John broke the silence. "I think we're due for a talk."