...OK, you probably knew this before I did, but I admit, I was surprised to find out it was...
Sherlock Holmes! He has been out on the moor the whole time Watson has been conducting his investigations and proudly sending reports back to Holmes.
I stooped under the rude lintel, and there he sat upon a stoneoutside, his gray eyes dancing with amusement as they fell uponmy astonished features. He was thin and worn, but clear andalert, his keen face bronzed by the sun and roughened by thewind. In his tweed suit and cloth cap he looked like any othertourist upon the moor, and he had contrived, with that cat-likelove of personal cleanliness which was one of hischaracteristics, that his chin should be as smooth and his linenas perfect as if he were in Baker Street.
While glad to see his partner, Watson is understandably pissed that Holmes has been doing his own detective work while making him believe he was actually contributing something. Holmes reassures him that his reports, which he's had forwarded to him at the hut, were indeed valuable, because they allow the two of them to compare their observations. Watson is persuaded, and ends up, as usual, admiring Holmes's cunning.
What interests me in this section is how closely Holmes is tied to the spookiness--the uncanniness--of the moors. Before he knows the identity of the man on the tor, here's how Watson describes him:
And it was at this moment that there occurred a most strange andunexpected thing. We had risen from our rocks and were turning togo home, having abandoned the hopeless chase. The moon was lowupon the right, and the jagged pinnacle of a granite tor stood upagainst the lower curve of its silver disc. There, outlined asblack as an ebony statue on that shining back-ground, I saw thefigure of a man upon the tor. Do not think that it was adelusion, Holmes. I assure you that I have never in my life seenanything more clearly. As far as I could judge, the figure wasthat of a tall, thin man. He stood with his legs a littleseparated, his arms folded, his head bowed, as if he werebrooding over that enormous wilderness of peat and granite whichlay before him. He might have been the very spirit of thatterrible place. It was not the convict. This man was far from theplace where the latter had disappeared. Besides, he was a muchtaller man. With a cry of surprise I pointed him out to thebaronet, but in the instant during which I had turned to grasphis arm the man was gone. There was the sharp pinnacle of granitestill cutting the lower edge of the moon, but its peak bore notrace of that silent and motionless figure.
This, combined with Holmes's odd, "cat-like" cleanliness while living in a hut on the moor, suggest that he's not exactly super-human, but maybe extra-human. Anyway, not human in the way Watson is. I wrote a few weeks ago about Holmes as an enchanter whose magic is reason. In these passages, Holmes appears as a spirit or specter, and perhaps some kind of sprite with dancing gray eyes. He may represent reason, but he's otherworldly all the same.
All this suggests that for all Holmes's brilliance, there is something not quite right about his enterprise. That notion is reinforced pronto, when, as he and Watson are comparing their discoveries of the past few weeks, they hear a terrible cry. Rushing to investigate, they find their client, Henry Baskerville, dead.
A low moan had fallen upon our ears. There it was again upon ourleft! On that side a ridge of rocks ended in a sheer cliff whichoverlooked a stone-strewn slope. On its jagged face wasspread-eagled some dark, irregular object. As we ran towards itthe vague outline hardened into a definite shape. It was aprostrate man face downward upon the ground, the head doubledunder him at a horrible angle, the shoulders rounded and the bodyhunched together as if in the act of throwing a somersault. Sogrotesque was the attitude that I could not for the instantrealize that that moan had been the passing of his soul. Not awhisper, not a rustle, rose now from the dark figure over whichwe stooped. Holmes laid his hand upon him, and held it up again,with an exclamation of horror. The gleam of the match which hestruck shone upon his clotted fingers and upon the ghastly poolwhich widened slowly from the crushed skull of the victim. And itshone upon something else which turned our hearts sick and faintwithin us—the body of Sir Henry Baskerville!
There was no chance of either of us forgetting that peculiarruddy tweed suit—the very one which he had worn on the firstmorning that we had seen him in Baker Street. We caught the oneclear glimpse of it, and then the match flickered and went out,even as the hope had gone out of our souls. Holmes groaned, andhis face glimmered white through the darkness.
"The brute! the brute!" I cried with clenched hands. "Oh Holmes,I shall never forgive myself for having left him to his fate."
"I am more to blame than you, Watson. In order to have my casewell rounded and complete, I have thrown away the life of myclient. It is the greatest blow which has befallen me in mycareer. But how could I know—how could l know—that he wouldrisk his life alone upon the moor in the face of all mywarnings?"
That last self-accusation by Holmes sums it up: he has sacrificed his client for the case itself. (Notice how he says it's the "greatest blow which has befallen me...": it's still all about him, isn't it?) One suspects, despite his expression of regret here, that he'd do the same thing again in a minute.
Conan Doyle seems keen on showing us that there are consequences to Holmes's single-minded brilliance. He is not a simple hero, a seeker and defender of justice. He is driven by ratiocination for its own sake, and anyone who hires him for protection risks meeting the same fate as Baskerville.
The character of the flawed detective is itself a cliche by now. But a detective whose very brilliance is a danger to his clients is compelling. Holmes himself is the "hound" of the Baskervilles--a spectral and seemingly supernatural hunter.