This could be a one-shot or multi-chapter story. I'm trying to imagine that Sherlock and Moriarty had met before. Reviews are very welcome.
Sherlock aged 11 or 12; Moriarty about 14 or 15. I believe Jim Moriarty's real name was Richard Brook. Thank you for reading.
In an empty toilet near the athlete locker room, a masked freckled boy with short black hair tried to keep his face straight while hiding a pair of sneakers into a large plastic bag – for lab use only- hastily. His rubber gloved hands moved with efficiency: he tied the bag and put it inside his backpack. Holding his breath, he took off his gloves and mask, put them inside another plastic bag, tied it tight and shoved it into his backpack, too. He would discard them later. The priority was to hide the poisoned sneakers of his archenemy. Carl Powers was pronounced dead an hour ago after suffering from an unspecified fit halfway through the race. A coroner's van just arrived. People thought it was an accident. The police chief in charge made an announcement that the loss of a promising young swimmer was very regrettable, but there was no foul play. Still holding his breath, the boy zipped his backpack, washed his hands, and got out of the toilet. He was heading toward the front door when a teenager bumped into him in the hurry to get inside. The boy yelped in alarm and dropped his backpack on the floor.
"I'm sorry. Let me help you."
The pale tall boy in school uniform emanated an air of being a head boy at a prestigious private school. He tried to pick up the backpack, but the small boy was faster: His hands clutched the backpack.
"Uh, I was just trying to help. Sorry."
"I'm good. Thanks."
"Sorry."
The teenager rushed into the hall and entered the room where most of police officers were investigating. Curious, the freckled boy followed the teenager. The door was ajar, and the boy could hear a commotion inside.
"Brother. Enough. Let's go home."
"Just listen, investigator. Check where Carl's sneakers are! All of his possessions were inside his locker, but not his shoes. Without them, how could he even get in here two hours ago? Barefoot? Before a swimming match?"
A low growling voice of an adult followed.
"I caught him checking on the dead boy's locker without permission twenty minutes ago."
The freckled boy got rigid, all of his muscles tense and his grin disappearing. Whoever that was, there was someone who had observed something suspicious.
"Ms. Mason, I'm so sorry. I'll take him home."
"Yes, I need to take the rest of the students back to the dormitory. Drop him off tomorrow before the class, please."
"Just listen to me. This might be a murder."
The teenager snapped in exasperation.
"You are helpless. I'll talk about this with father."
"I'm not playing a detective. Just listen. You'll see, brother."
The boy's voice was almost wailing.
He could hear people's footsteps. He hid behind a cabinet in the aisle.
"Officers, I'm sorry."
The teenager that had run into him minutes ago was literally dragging a younger boy - black curly hair, pale skin, tall for his age, 11 or 12 years old. The younger boy was struggling to break free.
It was so close. If any officer had listened to that brat…
The boy stared until the two brothers disappeared out of the door and then sighed in relief. The air was cool and breezy to his sweated face when he walked outside the building.
"Hey, Rich. Did you hear about Carl?"
One of the girls called out. Some girls, Carl's fans, were teary in shock; The close friends of Carl were blank-faced in disbelief. Richard gave her a terse nod, barely hiding a gleeful face.
Carl Powers had been his bully at school for years. Last Friday, he had run into Carl and dropped a cup of tea on his shoes "by accident". Carl was furious and ordered him to return the sneakers after making them as good as new before the competition. He spent three hours in cleaning off, washing shoelaces, and getting the shoes ready. This morning he had delivered them to Carl. He was so sure that Carl would love the pristine state of his sneakers.
He appreciated Aunt Page Brook: It was her lab where he had filched the poison. Dear Aunt Page, she believed that her nephew, Richard was aspiring to be a chemist. She would take Rich to her lab on Sundays when she had unfinished work to do. For years Richard Brook was a familiar, polite, and smart boy among the lab staff there so no one really watched him when he was around. A couple of months ago, Aunt Page taught him basic toxicology. He was all ears to her lecture especially when she talked about botulinum toxin. After three visits, Richard was able to sneak a very tiny amount of the toxin along with some safety items he would need from the lab without getting noticed.
When he was passing through the parking lot, he saw a trolly with a black body bag was being wheeled out to the coroner's van. Carl's parents were hugging each other on top of the stairs. Richard forgot about the annoying brat instantly; his face was elated from his first successful murder in his life. From tomorrow, his school life would be much better without Carl. He realized that a murder was more effective than any other methods that he had tried: teachers had pretended not to notice Carl's bullying and his parents failed to see how terrible his school life had been.
"Good Bye, Carl. I hope you enjoy your time in hell!"
Richard Brook disappeared into the streets.
Handling dangerous poisons like Botulinum toxin requires special apparatus like a fume hood: a few nanograms of the Botulinum toxin can be fetal, I suppose. I guess Rich was able to use it without getting a suspicion from lab staff because he had been around for years thanks to aunt Page;)