Chapter Text
Sherlock Holmes was bored.
To be fair, he was bored a lot.
The world was excruciatingly dull unless someone had been murdered, preferably in an interesting way.
“Have you read the paper?” John called out, flipping through the morning news. “Maybe there’s a nice murder in here for you.”
“Is there?” Sherlock looked up, mildly interested.
“Let me see.” John thumbed through the pages, but then his phone buzzed.
He glanced at it. “Well, no murder in the paper—but I just got a text from Greg:
‘23-year-old male, Jonathan, murdered. I’d like Sherlock to look it over—Scotland yard needs him on this (just don’t tell him). Unidentified poison found in the system. Victim also seems to have inhaled a toxic gas and there was a gas leak found. Please come. GL.’
How about that?”
“Hmm. Possibly a five. Maybe a six if the gas turns out to be creative.” Sherlock stood. “And I always enjoy showing up George.”
“It’s Greg.”
“Gavin. That’s what I said.” Sherlock smirked and reached for his coat.
They caught a cab to the crime scene, a quiet residential street shadowed by overcast skies.
As they approached the taped-off house, a nearby officer muttered, “Oh great, here comes the freak.”
John shot the man a sharp look, then glanced at Sherlock, expecting a trademark cutting remark. But Sherlock said nothing, his eyes fixed ahead.
John could swear he saw the faintest twitch in Sherlock’s jaw.
“Ah, Geoff,” Sherlock said brightly as they reached Lestrade. “Show me the location where the body was found. And the body itself, please.”
Lestrade exhaled through his nose. “This way.”
He led them inside a narrow, cluttered house. The walls were yellowing with age. Beer bottles littered on the kitchen table.
“We found him here, in the hallway. Neighbor called in, said they heard shouting.”
Sherlock didn’t respond. He was already scanning the floor, the walls, the light fixtures. His eyes gleamed with something close to delight.
“Definitely murder,” he said finally. “You checked for gas leaks, yes?”
“Yes. House is clear now. But how did you—?”
“Ah first mistake,” Sherlock began, pacing, “there are scuff marks on the floor—size twelve boots. Larger than the victim’s, whose shoes are still by the door—size eight, brown trainers, work shoes. Second, that chandelier above us has a fresh smear of blood—likely from a tall intruder hitting his head during a struggle. Looks like he is 6’5, but has a short stride. That could indicate a woman who wears heels a lot. And third, recent scratches in the key hole at the door, long and deep. Obviously a drunk trying to put the key in the hole. Could be from our victim, he is a suicidal drunk. His wife left him two years ago and took their only son with her.”
Greg opened his mouth to say something but decided against it.
John stepped forward, eyeing the chandelier. “Yeah, there’s dried blood. Didn't even notice. Dried… shouldn’t we figure out if it is as old as the body? Couldn’t the intruder have hit his head if he was planting a gas leak or something before committing the actual murder? Or did it happen at the same time?”
“Excellent, John.” Sherlock smiled faintly.
Lestrade grunted. “All right. Body’s outside in the ambulance. You’ll want to see this.”
They stepped into the cold light of the street. The ambulance doors were open, the body on a stretcher under a white sheet.
John suppressed a gag when the cloth was lifted. He’d seen plenty of bodies—but this one was off.
The man was stout, dressed casually, but his skin had a pale-green tint. A thin trickle of blood had dried at the corner of his mouth.
“He’s been dead about two and a half hours,” Lestrade said.
Sherlock leaned down and sniffed the victim’s lips, ignoring John’s look of disgust.
“The poison was ingested—still faint residue here. Anyone have a vial?”
An officer handed him a small sterile glass bottle. Sherlock carefully swabbed the man’s lips, collecting a drop of deep red liquid that smelled faintly metallic.
“What did you find in the house before you cleared it out?” he asked.
“We detected traces of hydrogen sulfide gas—pretty toxic in confined spaces. But there was no ongoing leak.”
“Hydrogen sulfide…” Sherlock stood, frowning in thought. “Combined with this particular compound, that’s... clever. I’m taking this sample back to Baker Street. I believe we’re dealing with sodium azide—an obscure poison. But it’s not fatal on its own. Not in that quantity.”
“So, what? The gas killed him?” Lestrade asked.
“No. The combination did. The sodium azide lowers blood pressure and respiration—slows the body just enough. The hydrogen sulfide shuts down the nervous system and olfactory senses. The victim wouldn’t even have smelled it before collapsing.” He paused. “A sophisticated kill. Likely timed or triggered after ingestion.”
Anderson appeared and Sherlock gave an audible sigh. Anderson spoke up, “So not suicide?”
The consulting detective gave an eyeroll. “As slow as ever.” Then Sherlock gave a cold smile. “Unless he force-fed himself sodium azide and filled his house with industrial gas? I highly doubt it.”
John raised an eyebrow. “Back to Baker Street?”
Sherlock nodded. “Time to experiment.”
The drive was short. Sherlock wasn’t very talkative—his mind already miles away, processing data, spinning theories.
John sat quietly, watching the familiar blur of London through the cab window. But near the end of the ride, Sherlock finally spoke.
“I believe the poison is not lethal on its own. Sodium azide—dangerous, yes, but not instantly fatal in small doses. However, combined with hydrogen sulfide gas… that’s where things get interesting.”
John glanced over. “You think it was some sort of chemical reaction inside the body?”
Sherlock nodded, eyes distant. “Not an explosion—nothing so crude. But the gas would have acted as a trigger. The azide slows respiration. The hydrogen sulfide shuts down the nervous system. Together, they could mimic a natural collapse—confuse even a competent coroner. But something went wrong, the body doesn’t look natural, the killer made a mistake.”
John frowned. “So the guy just... breathed it in? And dropped dead?”
“Roughly. But the method of delivery still eludes me. It had to be timed. Perhaps an automated release—or a chemical reaction set to begin after ingestion.” He tapped the glass vial in his pocket. “Either way, we’re missing the mechanism. And I have several experiments to run. First I want to see where the killer went wrong.”
They stepped out of the cab and into Baker Street.
John headed straight to his room, exhaustion tugging at his limbs. “Let me know if you figure it out.”
“I always do,” Sherlock murmured, already peeling off his coat and stalking toward the kitchen.
John woke to a thud.
Not a crash. Not glass. Just something solid hitting the floor.
He blinked at the ceiling, disoriented, half-expecting rain against the windows or distant sirens. But the flat was silent—unnaturally so.
And that was what bothered him.
He sat up slowly, listening. No violin. No pacing footsteps. No muttering. Just… nothing.
Frowning, he stepped into the hallway, bare feet cold against the floorboards. A faint chemical tang reached his nose as he passed the sitting room.
The kitchen door was half-closed. Light spilled out underneath.
He pushed it open.
Sherlock was on the floor.
One leg tangled under the chair. His left hand gripped a pen. His right twitched—barely. The notebook next to him was smeared, his scrawl slanted and loose.
His eyes were half-lidded, unfocused. A thin line of foam clung to the corner of his mouth.
John’s heart nearly stopped.
“Sherlock!”
He dropped to his knees, reaching instinctively for a pulse.
Still there. Weak, but there.
Sherlock’s head lolled toward him. He tried to speak, but his tongue didn’t seem to cooperate.
“S—symptoms…” he rasped, barely audible.
John’s eyes flicked to the notebook. It was a mess of timestamps, chemical notations, and increasingly shaky handwriting. The last line read:
"0.3ml = muscle weakening begins. Vision blurs. Gas = ???"
Next to it, half-written:
"Taste... not match. Alt formula—"
Then nothing.
“Bloody idiot,” John muttered, already grabbing his phone with one hand and checking Sherlock’s pupils with the other. “You dosed yourself? You dosed yourself while I was asleep?”
Sherlock tried to lift his hand, maybe to protest or wave him off. It didn’t make it past his shoulder.
John swore under his breath. The signs were clear—muscle failure, respiratory depression. Paralytic onset.
But Sherlock was still semi-conscious. That gave them a chance.
“I’m calling an ambulance. Don’t argue.”
He hit the emergency call button with one hand while using the other to gently turn Sherlock onto his side.
Sherlock’s lips moved again. “Timing... wrong... was... off... by...”
“Shut up,” John snapped, voice cracking. “You’re not clever right now. You’re bleeding stupid.”
Sherlock looked as if he was going to attempt to talk again but instead he vomited to his side. His chest hurt as his abdomen heaved.
But Sherlock’s eyes met his for just a second—glassy, dull, but defiant.
And then they closed.
John groaned, “Sherlock wake up, please!” His voice cracking and wavering on the last word.
John could hear his heart pounding in his ears, a deafening sound, while he answered the questions of the paramedic on the phone, giving the problem and address.
“Yes I know how to prevent asphyxiation, I’m a bloody doctor!” John felt bad when he hung up and yelled at the young women on the other side of the phone, but there were more important matters at hand.
Sherlock had regained consciousness and was freaking out. His brilliant blue-green eyes were sliding around.
“Not… lethal…” Sherlock moved his legs as if to stand up.
“Please Sherlock sit down. What do you mean not lethal? It looks pretty damn lethal to me!”
Sherlock didn’t respond, instead his shuddering breaths slowed. His head dropped to the side.
Paramedics burst through the door, on cue. An oxygen mask was applied, and Sherlock was stabilized.
After about an hour and a half Sherlock had returned to his normal colour and was unconscious on the sofa. Surprisingly enough, Sherlock was right, the dose he took was not lethal. The paramedics did all they could, and said Sherlock now just needs to rest. They also said that while he will survive and didn’t even need to go to the hospital, he may develop a fever later, but he will be okay.
John couldn’t believe how short-sighted Sherlock could be sometimes.