There's a lot of family in this short book. We start with Watson and his brother, then we encounter the Morstans, the Sholtos, and Jonathan Small and his adopted family of fellow conspirators with the child-like Tonga (very small; can't talk properly; er, also kills people with a blowpipe - I admit the analogy is not perfect). The book ends with the establishment of a new family as Watson gets engaged to Mary Morstan, who he has known for, what, two days? Of course, the point is to increase the dramatic effect as the reader imagines his or her normal family life being disrupted by the mistakes of previous generations, but I found it striking.
Sherlock Holmes has no family. (Mycroft and Vernet are in the future.) For him, as he says at the end, "there still remains the cocaine-bottle." I can't think of another novel which portrays the use of cocaine in such a positive light - "so transcendently stimulating and clarifying to the mind". In fact, I can't think of many novels about drug use at all, other than Philip K. Dick, William S. Burroughs, and Hunter S. Thompson, and even their more enthusiastic moments have a conscious sense of self-destruction about them. Again, Doyle is more subversive than I had realised. (And he has another, if briefer, go at the cosy relationship between the media and the police.)
I'm finding more in these than I had expected to. On to the classic short stories next.
Edited to add: new userpic is from a letter written by Arthur Conan Doyle to my distant cousin Frederic.)