The Adventure of the Creeping Man." The second story, albeit not explicitly, seems to completely disavow the first.
Holmes is hired by one Robert Ferguson in the matter of his wife, a native of Peru. He has on multiple occasions stumbled upon her apparently in the middle of abusing their infant son; on the most recent occasion, the blood on her lips and wound on the boy's neck implies she's actually engaged in some horrific act of vampirism!
Where the "Creeping Man" was a Jekyll/Hyde sort of story that embraced the supernatural in a thoroughly unsatisfying way, here in "Sussex Vampire," Holmes immediately dismisses the supernatural explanation as preposterous. From the moment they set out on their investigation, Holmes basically declares, "I'm not sure what's going on here yet, but there's no way it involves an actual vampire." Which is true, of course, and which makes the story Sir Arthur Conan Doyle had just written seem even more ridiculous by comparison.
The trouble is, the actual solution to this mystery is scarcely more realistic than an actual vampire attack would have been. (Spoilers a-comin'!) It's actually not terribly hard to guess -- when one strives to imagine any other reason someone might suck on an open wound, surely poison (in particular, a snake bite) is going to spring to mind. But the big ask here is that the Peruvian wife here is choosing to conceal the person (not herself) who deliberately inflicted poison on her own infant son.
We're meant to believe that this woman is so concerned for her husband's feelings toward his adolescent son from a previous marriage that she hides that the child is a masochistic freak abusing his infant half-brother. Absolutely ludicrous. I can think of no parent who would stand by for any reason and allow one of their children to repeatedly attempt murder on another. (And that's before you even factor in her lack of emotional connection to the stepson.) Plus there's the fact that she's risking being permanently separated from her child if she doesn't reveal the truth. And there's the matter that she told her maid the entire story, and that the maid doesn't feel compelled to disclose it either!
The resulting story is hugely unsatisfying, even if this time out, Holmes has a properly skeptical mind about things which seem to be supernatural in nature. This story hangs entirely on disbelief I can't possibly suspend, on the behavior of people that cannot logically be explained. As such, I have to rate it among the worst of the Holmes short stories. I give "The Adventure of the Sussex Vampire" a D.