Intro: London, 1989. Character details have been liberally reimagined.
The rare London sun for once emerged to bathe the sidewalks in precious warmth. Severus Snape hated the rare London sun. He hated towering over slovenly, dimwitted muggles who ogled at his imposing demeanor and long, flawlessly tailored black robes. Most of all, he hated abandoning his duties at Hogwarts School of Witchcraft and Wizardry in his quest for a cure to this oddest of afflictions.
A month had passed since the last onset - the memory drew shivers from his spine. Yet some relish arose and lingered from applying a healthy fraction of his generous salary to the fickle purse of intrigue, for the medicine Snape sought promised untold power and like all powerful men, Snape delighted in the acquisition of even greater power. The thought twisted his stoic features into a crooked grin.
The arrival of his destination snapped Severus out of his reverie. Step by creaking step, the warped wood of the stairs whined as if one more pound would shatter them - still they received his weight and did not break. The final step departed from him and he stood facing the door to 512B Baker Street. All he had to do was knock.
…
Sherlock Holmes peeled his lithe body from the barren wooden chair he was perched upon. The 1889 Afghan revolver clinked as he loaded it with a single bullet. At the fifth knock he set his jaw and beckoned his prey to enter.
The rigged door slammed shut and locked behind his house guest. Deductions flurried across Sherlock's supple mind. A professor. Chemist? The ash ingrained into he fabric of his cuffs suggested so, however the sides of his boots displayed a powderous resin inconsistent with any substance common to chemistry. Piece by piece the master detective tamed the brewing tempest of observation within him. His prisoner's merciless lips, though curled in confusion, betrayed an iron constitution unlikely to surrender easily. He raised the revolver, meeting his foe's gaze at the deadly level of a gun.
"You'll forgive the discourteous summons. Detective Sherlock Holmes, at your service." Holes spoke in a steady voice, but his blood was electric with the masculine heat of utterly dominating a worthy opponent. "But the enigma that has continued to vex me is who exactly you are. So -"
Then the impossible. Sherlock's fingers, seconds ago wrapped tightly around an 1889 Afghan, now grasped only at air. Peer across the room as if to coax some new metaphysics from that austere grimace, he saw the subtlest twitch of amusement dance along those unforgiving eyes.
…
Snape indulged himself in one delicious second of his opponent's doe-faced beguilement. Then he dealt with the non-magical pest. Gentle constricting Sherlock's shoulders to the floor with a deft spell, he knelt slowly over the helpless body and blocked the flow of oxygen through the long, slender neck gasping ineffectively under his large, strong hands. Holmes was athletic; against anyone else the contours he twisted into would have been the textbook ideal of evasive combat, but his physical competencies were rendered lame beneath the total submission of Snape's magic.
Thick and milk-warm, like the heft of cathedral tunes, a sonorous barotone poured from above into the choking figure on the floor, "Conniving muggle fool. You wish to know the last mortal face you shall ever witness? So be it - I am Snape, the Potions Master!"
His momentary fury pulled him into clarity. There was no need to kill this muggle. Anxious to depart, he sent whispers of sleep through his fingertips into Sherlock's lips. The full, moist flesh shuddered beneath his touch, still hungry for the blissful void of supernatural night. But the contact was severed. The aching wetness of Holmes' mouth settled into a quizzical frown.
Severus rose, his muscles convulsing, "No, not now. This-", his blood surged, sending a painful hardness throughout his body. The room was spinning now and all he could discern was the polite smile tracking his staggered lurch, until even that faded black. The death-eater mustered his consciousness before the seductive oblivion, and relinquished.
