With Neil Gaiman's Good Omens currently the strong contender for " non-Sherlockian characters getting the most attention at the next 221B Con," it seems like a good time to look back at the angels and demons inhabiting the original ACD Canon.
We have to first eliminate the angels-in-name-only, like the Avenging Angels and Hosmer Angel. And then we must eliminate those objects of male affection, Violet Smith and Brenda Tregennis of "Solitary Cyclist" and "Devil's Foot" respectively. It's more interesting when Sherlock Holmes refers to Violet DeMerville as an angel in "Illustrious Client, in comparing her to her "caveman" boyfriend, but still, doesn't seem too far from the woman-as-angels trope.
An even more interesting example of the trope comes in "Cardboard Box," as we get both an angel and a devil in one description: "There were three sisters altogether. The old one was a good woman, the second was a devil, and the third was an angel."
The one non-woman who gets called an angel by a potential love interest is Leonardo the strongman from "Veiled Lodger," whom Eugenia Ronder compares to the angel Gabriel.
And demons? You want demons? Jephro Rucastle could have the face of a demon. ("Copper Beeches.") Alec Cunningham was a "perfect demon" in "Reigate Squires." Josiah Amberley of "Retired Colourman" showed himself as "a misshapen demon with a soul as twisted as his body." No female demons in the Canon? Hmmm. Let's check one more spot.
Where we get our best Good Omens parallel for an actual angel and actual demon comes, of course, in The Hound of the Baskervilles.
John Watson wonders if the man seen silhouetted by the moon is a guardian angel when out on the moor with demon hound concerns. The convict on the moor was thought half animal and half demon by everyone but his sister, and given that there's supposed to be an actual demon hound roaming the moor, the possibility arises that the true hound of the Baskervilles was a female demon and that Selden the convict is actually a son-of-a-bitch.
The thought of an angel Sherlock and a human-transformed demon hound sitting on the moor and having a pleasant conversation about what is really going on around Dartmoor is the perfect Good Omens style scene. And kind of a nice one, at that, almost fitting the tale perfectly.
Man, if I was an artist, I'd totally draw that.