I've taken a LOT of liberties.
~ kittykittyhunter ~
The attack on Mrs Norris was still the talk of the castle, and as the Gryffindors marched towards the greenhouses, Hermione hissed, "But who could it be?"
Harry was again about to ask whether they believed in the Chamber of Secrets when he was distracted by a low cough. He, Ron and Hermione turned. They found themselves facing a dark-haired Ravenclaw boy; his eyes gleamed as he studied the group. At his side was a Gryffindor Harry only knew by sight: John Watson the third-year, who was usually seen a few steps behind his taller friend.
"Can we help you?" asked Ron hesitantly.
"No," broke in Watson, "but this idiot thinks he can help you."
The Ravenclaw didn't seem troubled by Watson's derisive tone; he waved a thin hand as though his intelligence was regularly disputed. "My name is Sherlock Holmes," he announced, "and for a price, I can name the Heir of Slytherin."
The footsteps of the other second-years had faded: Herbology would be starting any moment now. As politely as he could manage, Harry said, "Er… no thanks." He gave what he hoped was a neutral smile.
Holmes blinked. "You genuinely don't want to know?"
Watson rolled his eyes. "They genuinely don't want to know."
Ron (whose ears were starting to redden) shifted his weight. He rubbed his nose and then blurted, "Oh – go on then!" Sherlock smirked, but before he could say anything, Ron continued, "But we're not paying you for some mad theory –"
"Mad?" scoffed Holmes. "I base my judgement on fact."
"We really have to go," urged Hermione – but something in her tone suggested that she was dithering. "Professor Sprout is going to be angry, and –"
Holmes cleared his throat.
"Alright," rallied Harry, thinking that he would worry about the inevitable scolding at a later time, "what do you want?"
Watson's groan was ignored. "A simple favour," said Holmes. "I need, that is to say, I require –"
"Hurry up," growled Watson.
"– Help with my homework." Holmes turned his gaze upon Hermione, who immediately looked scandalised.
"Help you cheat?" she said acidly. "Unlikely! And aren't you a Ravenclaw?"
Holmes waved his hand again, as though this was a great inconvenience. "Does it matter? If I'm forced to worry about tedious things like homework – why, I may as well give up on education! No, my mind must feast upon more significant things…"
And he trailed away, looking off into the distance.
"Holmes," said Watson dully, "I should be in Transfiguration, and you're supposed to be in Ancient Runes."
"Quite right," nodded Holmes. "Very well – forget the payment.
"Now, as we are all aware, the attack on Mrs Norris, the feline belonging to one Argus Filch, occurred on Halloween. The majority of students were at the annual feast. However," Holmes smiled wryly, "three students gave their word of honour to a particular ghost that they would forgo the usual festivities, and attended a Deathday Party instead."
Harry wondered why they were being addressed in such a remote, detached way, but was advised (by a small shake of the head from Watson) not to pursue the issue.
"A student then departed from the feast prematurely," said Holmes. "Any excuse would suffice: having eaten enough, needing to go to the bathroom, unfinished homework… nothing prevented the culprit leaving the Great Hall, acquiring the paint that was necessary to daub the message and then escaping from the scene, quite unnoticed.
"Now, if we are in agreement that the feline in question is universally disliked –"
"Then," reasoned Holmes, "any person showing signs of distress must be treated with suspicion. Furthermore, we must agree that the attack was completed by a Gryffindor – yes, because the business of painting the threat was undoubtedly messy, and the student would need to wash her garments before retiring to bed. Finally, the height at which the words were painted assures us that the only magic involved was in the attack itself; I conclude that the attack was by a younger student.
Ron roared and punched Holmes in the face.