Sherlock's phone awoke them both. Buried somewhere beneath the pile of clothes they had so irresponsibly ditched on the floor, it buzzed insistently. John tumbled reluctantly out of bed and rummaged in Sherlock's pockets until he found the source of the noise.

"John Watson," he said smugly, looking back at Sherlock's wide eyes.

"Hey, John." Lestrade suddenly sounded unsure and somewhat nervous. "Where's Sherlock?"

"Right here. What's up?"

"It's a case," Lestrade replied grimly. "You'll want to be here as soon as possible."

"Why?"

Greg paused. "Kitty Riley's dead."

Kitty Riley lay flat on her back, staring up at the morning sky. She was on the pavement outside her apartment, surrounded by police and paramedics alike. There was an ambulance and stretcher waiting, but Greg was postponing their removal of her body. Her eyes still shone, and if her lips had not been so blue she could still have been alive.

When Sherlock caught sight of her limp form John could have sworn he saw him baulk. Sherlock had never been disturbed by a dead body before – not by mutilations, gore, or even children – but when faced with this ever so familiar corpse he seemed shaken. "How did she die?" His voice was low and quiet.

"Heart attack," said Greg. "Apparently she had a history of heart problems. Went in for surgery last year to put a stent in." He looked down at her with disgust. "Can't say I'm sad to see her go, after what she did to you."

"If she died of a heart attack, why did you call me?"

Greg pulled out a rumpled sheet of paper from his pocket and held it out to the detective, who took it in one gloved hand. "I thought this might mean something to you."

Sherlock barely glanced at the words, immediately turning the paper over in his hands and holding it to the light. His keen eyes scanned every inch of the paper within seconds. "Fingerprints?"

"I haven't checked yet," Lestrade admitted. "That's why I was wearing gloves. But you'll find hers on them – she was holding this when she had her heart attack."

"Send it back to the lab," Sherlock commanded, handing it back and walking over to Kitty's body with a blank expression.

"What does it say?" John asked Greg whilst Sherlock crouched over the journalist, magnifier in hand.

Greg handed it over wordlessly. Three words were printed on the page, apparently by a typewriter. Give yourself up, it said. At the bottom it was signed SM. John's throat squeezed as he turned back to Greg. "Sebastian Moran?"

"Maybe. Everyone else is ignoring it because they think it was a message for Kitty."

"This is why you called us?"

"You have history with her," Greg shrugged. "And you're under threat."

John's jaw clenched. "You think this message is for me?"

At that moment, Sherlock returned. "Anything?" Greg asked hopefully.

"Nothing," Sherlock practically spat. "Nothing out of the ordinary or unusual."

"It was a heart attack, Sherlock," the doctor said gently, resting his hand on his husband's arm. "What were you expecting to find?"

"Something! Anything!" Sherlock growled. "Something isn't right, John. I don't know what – there's nothing telling me that there is except –"

"A feeling?" John finished.

The detective's lip curled. "There's no such thing as coincidences, John, and I am not willing to bet your life that there is."

"He wants me to 'give myself up'," said John.

"Of course he does. He knows he can't get to you whilst Mycroft and I are protecting you."

John looked back at the paper. "What happens if I don't?"

Sherlock crinkled his nose. "Nothing good. But there's nothing we can do about that." He placed a hand on John's shoulder firmly. "Lestrade will take you home."

"I don't want to go home, I want to help," the doctor protested, sweeping Sherlock's hand away.

Sherlock's expression softened, leaving on his face the clearest adoration. "I know. And I would give anything to let you, you know that. But Bart's isn't safe, and even you being here sets my teeth on edge. Please, John. For me. Just go back to Baker Street."

He considered this for a moment. He watched Sherlock's eyes dart frantically between each of his own, full of anxiety, and he deflated. "Alright. But I'm not going to sit around, Sherlock."

The detective planted a quick, hard kiss on John's forehead. "Of course not. You're going to look into Miss Riley's medical history, find out who her doctors were when she had the surgery. Molly will send you everything through Lestrade."

"Do I get a say in this?" Greg asked stubbornly.

"No," Sherlock answered bluntly. "Look after him."

"Of course I will," the DI replied. "Sherlock, you don't have to be so overprotective all the time –"

John waved it away. "It's fine, Greg."

"But –"

"It's fine," the doctor said emphatically, cutting him off. "I'll be more useful to him at home anyway."

Greg took John back to 221B in the back of the police car. Donovan was sat in the passenger seat, flicking through the small number of evidence bags she'd managed to pick up from the scene. Her focus rested on the note, silent in expectation of an explanation. John did not bother giving her one. For the moment he couldn't trust anyone with any information, including Sally.

The three of them were silent for the entire trip. Lestrade was jumpy, as though the next car to come around every corner contained Sebastian Moran armed with a machine gun and a grenade. When they pulled up by the black door with its golden knocker, John didn't say a word. He just got out of the car and walked up to the front door.

"I'll be back!" Greg called out through the window. "Half an hour max."

John did not look back at him.

As soon as he'd stumbled through the door Mrs Hudson scooped him into a tight hug. He hugged her back, breathing in the scent of washing-up liquid and dusting spray.

"Where's Sherlock?" she asked.

"He's got work to do. Doesn't want me in the way. Either that or he doesn't want me getting hurt," the doctor answered bitterly.

Mrs Hudson slapped him on the chest. "You don't have to be so sour, John. Sherlock's only doing his best."

John shook his head. "I'm not… Sour, Mrs Hudson. I just wish…"

"It's alright, love." She placed one soap-sudded hand on his cheek. "It'll sort itself out."

"Yeah."

When he reached the top of the stairs, everything suddenly went heavy. His legs were like lead weights, and his arms hung uselessly by his sides, unwilling to move. More could be said about his heart, and the way it ached inside his chest as though it were a stone lodged deep inside him.

When the rest of them arrived at St Bart's, Sherlock jumped out without waiting for Lestrade to put the handbrake on. The DI turned to Sally apologetically. "Stay here."

"But –"

"Just do it."

Donavon reluctantly complied, and Lestrade jogged to keep up with the Holmes' long, purposeful strides.

"Molly texted me. Miss Riley's body arrived five minutes ago. It should be a couple of hours until she's finished."

Lestrade frowned. "A couple of hours?"

"That's what I said, Detective."

"What are we meant to do while we're waiting."

Sherlock shot him a sly sideways glance. "Play Scrabble. Watch 'Scrubs'. Have phone-sex with my brother; whatever you would like to do, Lestrade."

"That's not –"

The consulting detective hissed in frustration. "Not half an hour ago I told John that you'd take Kitty Riley's medical records to him. Perhaps you remember that, Gordon?"

"It's Greg."

"Greg."

The DI resisted the urge to roll his eyes. "Fine."

"Molly's laid them all out for you. Get them to John, then come straight back. I'll need you in the lab."

Lestrade frowned. "I don't know anything about lab stuff."

"Don't worry, you'll do fine," Sherlock assured him. "Just do as I tell you."

When they arrived, Molly didn't even look up as she made a long cut through the flesh of Kitty Riley's abdomen. "Paperwork's over there." She waved in the general direction of the table with her scalpel.

"Hey, Moll," Lestrade smiled, meandering over to her.

Molly jerked her head up in surprise. "Hello, Greg. Wasn't expecting you."

"Sherlock's got me running errands. Not sure if I'm meant to be doing something more productive, as a police officer, but needs must I suppose."

As though to prove his point, Sherlock snapped his fingers impatiently. "Get a move on, Lestrade."

Greg shot Molly a sideways glance and an eye roll. She bit her lip and grinned, trying to hold back a laugh. "Have fun!" she called after him as he picked up the folder and left with a tip of his head.

When Lestrade was safely out of sight, Sherlock turned to Molly. "I need everything you've got so far," he hissed. "Blood samples, tissue samples, skin cells, theories… Everything."

"I've bottled everything up for you. It's in the fridge," Molly reassured him, trying to calm the nerves that were so obviously making him incredibly jumpy. "As for theories, I have no idea. You'll have to take a look yourself."

"Gloves?"

She handed him a pair, and he took them without his eyes ever leaving Kitty's innards. Molly hesitated, as though she wanted to say something, but she simply closed her mouth and continued working. Sherlock watched her patiently. Her deft, steady hands were a comfort. Steady hands were a sign of intense calm, and Sherlock needed calm. He was too stressed, he knew it, and he was taking it out on her and on Lestrade. Had John been there… But he couldn't be. It was time to switch off. Pretend it was a normal case. Compartmentalise.

His eyes flashed, searching for a fault, a disfigurement in the anatomy. A slight discolouration, a hole or a clot that wasn't supposed to be there, any signs of poisoning. He gritted his teeth, finding naught. Molly packed organ after organ into retainable containers, but Sherlock found nothing of interest in any of them.

"The heart, Molly," he said after an hour of futile scouring.

"Alright," she huffed.

Sherlock flinched. "Sorry," he mumbled, ashamed. "It takes time, I know."

Molly smiled. "It's alright. It's no problem."

Heart surgery, Sherlock thought as Molly peeled away skin and muscle from the ginger woman's still chest. The doctors had presumed it had been natural, but had it been induced? To induce an attack in someone who already had heart problems would be only too easy.

"Give me the rib spreader," Molly commanded. Sherlock passed it eagerly, his keen eyes watching intently.

With a delicious wet sound, the journalist's heart was exposed at last. It lay, deadweight, in its assigned space, innocent and slightly purple. "Sherlock, why don't you sit down whilst you're waiting. I have to do this properly, so it'll take a while."

"Molly," Sherlock said with all severity. "You need to be looking for the stent."

Molly frowned. "What makes you so sure? It could've been any of the other vessels."

Nonetheless, Molly checked for the location of the stent. "It should be in the pulmonary artery. But…"

"It's not there?" Sherlock guessed.

"I don't understand," she said slowly, continuing to search. "It was right in her paperwork. Stent. Pulmonary artery. Three-quarters of an inch away from the ventricle."

"Take some tissue samples from where it should be and give them to me."

"What, now?"

"Yes, now," he huffed impatiently.

"I won't help you if you're going to be pushy."

Sherlock bit his lip anxiously. "I'm sorry, Molly."

"Here."

It took less than five minutes for Sherlock to whisk himself off to the lab that St Bart's had lent him for use and set up the correct equipment. He wasn't entirely sure what he was looking for, but his first port of call was the material of the stent. If it had been made of some sort of biodegrading material, it would explain its disappearance and Kitty's subsequent heart attack.

When the results came back, Sherlock threw the petri dish – artery segment and all – against the wall, and watched its shining fragments scatter across the floor.

Then an idea occurred to him. The stent, such a small, thin mesh. It seemed inconceivable that it could have been carrying… a poison? No. That would be impossible. The stent would have to have fragmented, and its careful design would've prevented that in the first instance.

Sherlock plucked another slice of artery out of the set of samples Molly had given him, and set to work.

"It was the stent!" Sherlock crowed as he re-entered the morgue, where Molly had her hands full of lungs. She jumped quite viciously and almost dropped them.

"Sherlock!"

The detective ignored her shocked expression. "It was the stent itself, don't you see? A murder device inserted into Miss Riley's body in such a perfectly legal and convenient way that most people would only see a heart attack but this, oh no, this was no natural heart attack. Kitty's own heart problems are completely unrelated, of course. Any other person might have been given the same stent and died in the same way, but her cardiac issues were just an excellent coincidence that would further help to cover up any scandal or hint at murder in this case.

"It was a murder, but one long in the making. Kitty was a marked woman the moment she cornered me in the bathroom in the courthouse, but she was only ever a dead woman walking when she went in for heart surgery last year. The stent that was put into her pulmonary artery following a severe heart attack in August last year was the murder weapon. The polymer that it was made of allowed that there could be a miniscule tube inside each fibre, and inside those tubes was a poison – botulinum."

Molly's mouth dropped open. "You mean…?"

"Our friend Sebastian is being poetic, yes," Sherlock said breathlessly. "He's copying Moriarty, which would be a stupid decision in any other case – sentimental, naturally – but we already know who he worked for and what his motives are. And botulinum was the most logical choice, considering that even in incredibly small quantities it still has lethal effect.

"But the toxin couldn't have been released without the stent having broken, which it's designed not to do. Which is why the stent was attached to a tiny detonation device which was implanted beside it, but it was never mentioned in the report, obviously. The device could be activated remotely, so when Moran saw fit to kill Kitty Riley, all he had to do was press a button."

If there could have been anything less satisfying than the whiteness of Molly's face in that moment… Sherlock knew what she was thinking. It wasn't a difficult leap to resolve that there was, somewhere in St Bart's, was a doctor who was killing people.