I've had lots of little 'what-if' prompts floating around in my head lately, but this one is definitely the most persistent: What if Mary hadn't taken the bullet meant for Sherlock? Also, it looked like she moved after the shot was fired, which is kinda impossible, but that's not as important. Throughout season 4, we got to see John's reaction to losing his wife and how it affected his relationship with Sherlock; this story is the other way around. I must warn you it's a real heart-wrencher, but if you're reading this note you've already seen the summary/warnings and decided it was worth checking out. Anyways, enjoy!

Chapter 1: Cataclysm

John didn't see it happen. He heard the gunshot as he ran through the aquarium. Glass fish tanks took up most of the wall space, and he didn't hear anything shatter… so odds were the bullet didn't hit the wall. He tried not to think about what it could have hit as he rounded the corner and burst into the room. Mycroft bustled past him with his phone to his ear, a look of barely-restrained panic on his face. John had never seen Mycroft panic. There was only one thing—one person—that ever elicited any sort of emotion from the British government.

John scanned the room, but anything he may have observed about the situation was immediately deleted when he saw where the bullet ended up. Back in Afghanistan, he'd been able to remain level-headed and calm no matter the degree of crisis. Two men both shot and bleeding out on the sandy desert floor? No problem. An explosion rendered five soldiers clinging to life? Captain Watson could handle it. But Sherlock Holmes takes one bullet and all of John's medical knowledge abandons him. This was now the second time he'd stumbled into a room to find his best friend bleeding out on the floor. However, last time he'd had only a concussed Charles Augustus Magnussen for company; now he had a room full of spectators to watch him fall to pieces.

Mary looked up at him from where she crouched by Sherlock's side, both hands pressed firmly against the wound in an attempt to staunch the blood flow. His wife, who'd been responsible for this last time around, now silently called him to help, to do something, to fix this. But as John got closer and knelt down beside Mary, he knew there would be no fixing this. The damage was catastrophic, blood pouring from Sherlock's chest at an alarming rate despite Mary's efforts.

"Jesus, no," John heard himself whisper. At the sound of John's voice, Sherlock looked up at him, eyes glazed with pain.

"John," he mumbled.

"Shhhh, you're okay." Mere seconds ago, John had been drowning in panic, but somehow, hearing Sherlock call out to him chased the sensation away, leaving behind an ethereal calmness for which John was immensely grateful. The pain could wait until later, Sherlock needed him now. Wordlessly, he and Mary switched places. "You're okay. Remember last time? They fixed you up and you ended up fleeing from hospital."

Sherlock clenched his eyes shut and shook his head back and forth. "Not like last time." John knew he was right. He didn't want him to be right—he desperately wanted him to be wrong—but of course Sherlock was right. No ambulance could get here fast enough, even if they'd called minutes before the shot had been fired. John could feel Sherlock's very life force pulsing out from the hole ripped in his chest.

"Okay," was all John could muster. "Okay."

"John?" Sherlock weak voice was barely audible over the sound of John's own heartbeat reverberating inside his head. "Not Bart's," he coughed, and a trickle of blood spilled out of the corner of his mouth. "Not Molly."

Oh God. In his dying moments, Sherlock was thinking about poor Molly Hooper. His breaths were numbered, and he used one to tell John not to let his dead body be deposited at their friend's workplace. He didn't want her to see him when it was all over. When his life was over.

"Okay," John assured. "Not Bart's. God, you're a saint, you know that?" At this point, Sherlock was spluttering, barely able to get air into his failing lungs. John bit into his own lip hard enough to draw blood. For the second time in his life, he had a front row seat to his best friend's death. He remembered the feeling of helplessness that had overcome him upon seeing Sherlock broken and bloodied on the pavement all those years ago. He'd been too late to stop Sherlock from jumping, and he was too late yet again. If he'd gotten here just a little bit sooner, he could've stopped this. But there would be no miracle return this time around. There was no opportunity for tricks, no switching bodies. This was real. And it was ripping John apart.

"Sherlock, you made a vow," John croaked, remembering what he'd been promised at his wedding. "You said… you said you'd always be there… whatever happens." In the middle of that sentence, the tears came. John tried to hold himself together, but there was no stopping the flood.

"You'll still… have Mary," Sherlock reminded him. For an instant, John looked at the woman he'd made his wife. Yes, he would still have Mary. But she wasn't enough. She would never be enough. John didn't want to settle down into family life with his wife and daughter. He wanted to chase criminals around London, listen to marvelous deductions, and find strange specimens in the fridge. He wanted Sherlock.

"But I want you too," John whined. He honestly didn't care if he sounded childish. He was living his worst nightmare, and he was bloody terrified.

"I'm sorry," Sherlock sighed. John looked into those beautiful blue-green eyes and saw true remorse. Rarely did Sherlock apologize for anything, and knowing he regretted this brought fresh tears to John's eyes.

"Don't apologize. It's not your fault." John carded his free hand through Sherlock's curls, and memorized the pattern of multi-colored flecks that adorned his irises. Soon those eyes would close, never to open again—John halted that thought process before it went too far. Sherlock turned his gaze to Mary and instructed:

"Look after him."

"I will," she assured, squeezing Sherlock's left hand before letting him return his attention to John.

"John." Sherlock could barely speak, and John was forced to lean closer just to hear his whispered words. "Take care of Rosie." John nodded, but his daughter was the last thing on his mind when Sherlock was literally dying. She would be fine. She would grow up never knowing her godfather, but she would be fine. John, on the other hand, could feel his sanity trickling away from him faster than Sherlock's blood through his fingers.

Sherlock, infinitely observant despite the trauma, clearly saw John's distress. "You'll be okay," he assured. He took John's free hand, the one that wasn't still futilely plugging the hole in his chest, in his and weakly squeezed it.

"No I bloody won't!" John cried, clinging to Sherlock's hand as if his grip alone could keep the detective tethered to life. He felt Sherlock's thumb circle the back of his hand. Somewhere in his mind it occurred to him that he should be the one comforting in a situation like this, not the one needing to be consoled. But the majority of him was focused on the overwhelming rush of emotions: fear, regret, anger, and sorrow.

"John, promise me." If possible, Sherlock's voice was even weaker, the faintest whisper of words in the appalling silence of the aquarium around them.

"Promise what?" In that moment, John would do anything Sherlock asked. He'd leap out of a plane without a parachute, or dash in front of a speeding train. He'd hurl himself off the roof if Sherlock asked him to. Any of those things would get him killed, but at least he wouldn't have to live with the gaping hole in his side that Sherlock's absence created. He'd done it once for two years, and it had nearly driven him to madness.

"Promise you'll… move on. Live your life." Oh God, anything but that. John Watson could've done anything in the world but that. When Sherlock died the first time, his world came crashing down around him. He'd just finished building it back up even greater than before, and now it would be razed to the ground yet again. But he couldn't deny Sherlock this. He'd asked John to promise, so he would try his absolute best despite the despair eating him up from inside.

"I promise," John said, holding Sherlock's right hand to his chest. He met Sherlock's gaze one last time before his eyes fluttered shut. Those bright blue eyes that saw infinitely more than John could ever hope to observe closed for the last time. John subconsciously shifted his grip to feel Sherlock's radial pulse. The same hand John had floundered for last time, searching for any hint of life despite knowing the truth. The same hand that had told John firmly that its owner was dead, even when he wasn't. He detected the faintest beats of Sherlock's heart—hopelessly weak and erratic, but there. He closed his eyes and counted each and every one, holding his breath in between.

One.

Two.

Three. Four.

Five.

Six. Seven.

Eight. Nine.

Ten.

Eleven.

Nothing. John's eyes snapped open, and he adjusted his grip in hopes of finding it again, but there was nothing to find. Sherlock's heart no longer beat within his chest. Oxygen no longer journeyed to that magnificent brain. He was gone. Eleven beats. That's all he'd had left to give. Just to be sure, John searched Sherlock's armpit for the little ball that people sometimes used to cut off the pulse. Finding nothing, he checked his findings again at Sherlock's neck. Nothing. He watched his chest, waiting for another rise to indicate he'd taken a breath. Stillness. John heard a pained, animalistic whimper. It took him a while to register that the sound had come from his own throat.

Next thing he knew, he was seated next to Sherlock with his arms wrapped around his already cooling corpse, the detective's head tucked in to rest on John's shoulder. If it weren't for the massive red stain on Sherlock's shirtfront and his ethereal stillness, he could've been napping, with John for a pillow. He knew it was mad, knew that this degree of attachment was disconcerting, but he didn't care. He breathed in and out slowly, his nose still able to detect the smell of Sherlock beneath the salty tang of blood. Rosin and shampoo with the faintest hint of the musk John associated with 221B Baker Street. He smelled like home.

For a moment, he imagined they were home, crashed on the couch after a particularly exhausting case. They'd done it before, fallen asleep practically on top of each other because they were both too tired to move another inch or to care about the implications. If he listened closely, he could almost hear the sound of Sherlock's gentle snoring. John was content to remain there forever, but he knew he wouldn't be allowed. Someone would come and take Sherlock—Sherlock's body—away from him. Then he'd really be gone forever.

John nestled even closer, clenching his eyes shut. If he opened them, he'd see everyone in the room staring at him with a mixture of pity and fear. He'd see the wound and the blood that reminded him that they weren't safe in Baker Street, they were slouched against the wall of an aquarium with his ex-assassin wife and a madwoman with a gun. A gun that had killed Sherlock.

Was it really the gun that had killed him? Or the bullet? Or Vivian Norbury herself? All were crucial parts of the murder, but if he had to pin the blame on one, which would it be? The bullet—the projectile—that flew at mesmerizing speed and buried itself deep in Sherlock's chest, opening up countless vital blood vessels. The gun that contained that bullet and provided the power to launch it at such speed. The woman whose twisted sense of purpose led her to sabotage a coup, and whose need for the last word made her fire on an innocent man. Or Mary, whose secret past life brought John and Sherlock into this insane web. If it weren't for Mary, they wouldn't be here. But the same would be true if it weren't for John falling for and marrying her. He'd been vulnerable when he met her, still reeling from Sherlock's first death. If he hadn't been such a hopeless romantic, if he'd somehow seen her for what she really was, they wouldn't be in this mess. Without a doubt, it was his weakness that inevitably led to this. Sherlock was dead because John couldn't bear to be alone in the wake of his best friend's suicide. So Sherlock was dead because Sherlock was dead—how strange.

"I've really lost my mind this time," John muttered. "Sherlock, why aren't you calling me an idiot?" He opened his eyes and glanced over at his friend. "Right, 'cuz you're dead," he chuckled. Then he realized he was laughing at his friend's demise, and laughter instantly morphed into sobbing. He buried his face in Sherlock's shoulder and wept. He wept for hours, or maybe it was only seconds. Time simply didn't matter when Sherlock wasn't around to lose track of it.

John was too absorbed in the moment to notice the arrival of the paramedics. He sensed the extra pairs of eyes trained on him, but he didn't react. Nothing mattered right now except him and Sherlock. But he was forced out of his reverie by Mary whispering his name insistently. Reluctantly, he lifted his head from the fabric of Sherlock's coat. He glanced at the medics, noting the combination of puzzlement and concern etched on their faces. He wanted to scream at them for being too late, for failing to save Sherlock. They were summoned to save a life, but they arrived instead to cart away a corpse.

But John had to admit it wasn't their fault. Countless variables factored into their travel time, and even an ambulance with sirens blaring could only drive so fast. Even so, John was still angry with them because they would soon take Sherlock away from him.

"John, you need to let go," Mary's gentle voice pierced through the fog of John's anguish. He knew she was right, but he didn't want to let go. Last time he let go, they carted Sherlock off and he disappeared for two years. If he let go this time, he'd disappear forever.

"No," he told Mary, hugging Sherlock closer. Somewhere deep down, he knew he was being irrational, that he couldn't sit here forever and pretend none of this ever happened. But that part of him was silenced by the part still in denial.

"John." Mary sounded worried now. "You have to let him go."

"No." Hot tears rolled down his cheeks, but the sensation barely registered with the screaming agony in his heart. He couldn't let go, neither physically nor emotionally. Twenty years from now, thirty years from now, he would still cling to Sherlock.

"John." Mary crept closer and sat on John's other side. He was reminded of something Sherlock said at their wedding: "Today you sit between the woman you've made your wife and the man you have saved." Well, now he sat between his wife and the man he failed to save. Mary rested a hand on John's thigh and tried to coax him into looking at her. "John," she repeated. He looked into her eyes and saw fear; she was afraid of his behavior and what it revealed about his state of mind. She'd seen him grieve for Sherlock before, and she'd helped him through it. But John and Mary hadn't met until a few months after, when the wound had scarred over. She'd never seen him as raw and broken as he was now. He'd never felt as raw and broken as he did now.

Last time had been awful—the worst day of his life—but this was definitely worse. The first time, Sherlock ended his own life. John was devastated, but if Sherlock truly didn't want to live in this world, he shouldn't have to. He chose to die. This time, life was brutally ripped away from him. He didn't want to die. Though he didn't often show it, John knew Sherlock was happy. He'd been rescued from exile and given a second chance. He was godfather to John's daughter. He was the most famous detective in the world. Now that title would go to someone else, and Sherlock Holmes would go down in history.

He sighed in defeat and relinquished his grip on Sherlock. He hugged his knees to his chest and put his head down, not daring to watch. He heard the small scuffle and knew what was happening, but he refused to acknowledge it. But suddenly, his left side was cold and only Mary remained beside him. Sitting next to his loving wife, John Watson was lonely.

"Goodbye John." He heard it as clearly as he had over the phone years ago. Sherlock's voice resonated inside his head, bouncing off the walls of his skull. But instead of watching Sherlock plummet four stories, he himself was plunged into freefall. He saw snippets of memories flash before his eyes: meeting Sherlock for the first time, the pool incident, the Woman, the hallucinogen-fueled meltdown in Dartmoor, the Fall, their less-than-happy reunion, Sherlock teaching him to dance before the wedding, breaking into Magnussen's office, their conversation on the tarmac before the almost-exile, the birth of his daughter. Every important event in John's life included Sherlock. How was he supposed to continue living if he was gone?

1. I'm sorry. I'd like to say that was the worst of it, but I'd probably be lying.