A Study in Green & Silver (смешанная)

The Inter-House Challenge: also known as the bane of John Watson's existence. He turned the card over in his hands once more- emerald green, the stock heavy- and eyed the spidery silver scrawl on it with more trepidation than seemed reasonable. A lot of other boys were mentoring Slytherins, so why should he be so nervous?
John sat down on the edge of his bed, the card in his hands, and stared at the name written there. If he were honest with himself, he knew he wasn't worried because the boy was a Slytherin, or a pureblood, or wildly wealthy. He was worried because the boy was Sherlock Holmes.
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Follows a similar plot to A Study in Pink. John is a sixth-year, Sherlock a fifth-year, but that doesn't mean that Auror Lestrade doesn't need their help once a wizard begins poisoning Muggles in what Muggle police falsely believe to be serial suicides.
COMPLETE & PROOFED.