The second Sherlock Holmes novel is, like its predecessor, A Study in Scarlet, more of an adventure yarn than a detective story. Some 50 years after Poe invented the genre in The Murders in the Rue Morgue, Conan Doyle is still feeling his way. The crowd-pleasing element of the Holmes stories - the detective's astonishing ability to solve a case by piecing together scraps that, to lesser brains, wouldn't even constitute clues - is thrown away in the first of this novel's three sections. With Holmes having solved the murder, the second section deals with the hunt for the killer, while the final section contains the killer's thorough and somewhat implausible confession.
What makes the novel interesting are the oddities of Holmes's character. The book opens and closes with him taking cocaine and Watson warning him of the habit's health risks. It's one of the ways Holmes deals with being bored. All detectives need a quirk, of course, but this is a step up from Rebus's boozing.
My edition of this book is Leslie Klinger's annotated Sherlock Holmes, which adds all kinds of information to the story, not all of it welcome. While many of the footnotes illuminate obscure terminology or historical references, some are based on Klinger's decision to treat the stories as if they really were written by Dr Watson and merely published by Conan Doyle. Though cute at first, this becomes very irritating as Klinger adjudicates between various sources as to the precise date of this adventure.
The story itself is deeply silly. The murderer is, for example, a cannibalistic pygmy armed with a blowpipe. Still, it's a significant step in the development of the modern detective story.