Although I am very aware of the Sherlock Holmes scenario in the first two editions of Gaslight, and how little the themes of SH fit with HPL's vision, I am also convinced that many SH stories could be (at the very least) good foundations on which to write a CoC scenario.
In addition to using SH stories as "Victorian English society -101", almost any SH story could be adapted to serve as a change of pace, non paranormal scenario.
However, a very select few, can (I believe) make good foundations for CoC. For example:-
Speckled Band - Woman dies in her bedroom, raving about "A Speckled Band". Her sister is now forced (by her stepfather) to sleep in the same room and has been hearing weird noises in the night. SH investigates and uncovers clues that stepfather (from adjoining bedroom) is sending a poisonous snake (the Speckled Band) through a ventilation duct into the bedroom to kill the sleeper there. Wants to kill two stepdaughters to get his hands on their inheritance. Obviously for CoC the snake can be replaced with any minor Mythos servitor (or be a Snake of Yig?) which is somehow being introduced into the bedroom by the stepfather.
Devils Foot - Siblings living together in a cottage found one morning - two brothers maniacally insane and sister dead.Their estranged brother mentions that he had visited them the previous night and one brother had seen a frightening figure moving outside (which he blames on the devil!). SH discovers killed by a poisonous root thrown onto the fire by the estranged brother. Again, any minor Mythos entity could suffice to scare them to mania or death - or, as a non paranormal scenario it can just be the poison.
Musgrave Ritual - Stately home Butler vanishes but leaves behind clues he was researching a historical riddle belonging to the noble family he serves. SH investigates the riddle/ritual and traces butler to secret room which hold the butler (dead) and the reason for all the secrecy - Charles the First's crown! Obviously the secret room can hold a Bound entity (hence the secrecy) which is a good reason to find the butler dead. But the ritual /riddle could seem to point to some treasure so tempting the butler in the first place.
Anyway - I am sure there are more - but that's enough from me for now.