I was afraid that the second episode of Sherlock might not live up to the first one, but I need not have worried. In fact, I think the mystery and overall plot was even more intricate and complex than the one from "A Study in Pink". It certainly took me a lot longer to identify the canon references. Actually, I'm sure I didn't get all of them and the assumptions I've made could very possibly be wrong.
When the first cypher appeared, along with the first body, I found myself going back and forth between The Sign of Four and "The Empty House". I thought The Sign of Four might be a possibility as a "sign" was left with Major Sholto's body, and Jonathan Small scaled up the side of Pondicherry Lodge after Tonga throws down a rope. And "The Empty House" crossed my mind because Ronald Adair is found shot in his room when the door was locked from the inside. Oh, and Sherlock's university friend is named Sebastian, which made me think of Colonel Sebastian Moran.
After we hear Soon Lin Yao's story about her connections to the Black Locust, I was sure the writer was referring to "The Dancing Men" because Elsie Cubitt flees from America to England to escape the mob connections of her family. Then, like Soo Lin Yao, she begins to find coded messages and knows that her past has caught up with her. Finally, when I learned that the cipher involved numbers and the key was a particular book, I decided that we were dealing with The Valley of Fear. Not only that, but we learn at the end of "The Blind Banker" that Moriarty was behind the smuggling operation. Well...I'm beginning to suspect that "The Blind Banker" involved elements from more than one Conan Doyle work and that I probably didn't catch them all.
While all of these mental gymnastics on my part might seem boring, frustrating or, even, maddening, I had fun trying to work out the references. Thanks to puckrobin, I was able to listen to a great interview with Mark Gatiss in which he explains that the Basil Rathbone films (which also borrowed elements from canon) were one of the inspirations for Sherlock. Gatiss cited The Pearl of Death as an example, for the movie takes part of its plot from "The Adventure of the Six Napoleons". Of course, fans of Rathbone have a much easier job working out the canon references as any material taken from Conan Doyle is mentioned in the opening credits of each film. *g*
Aside from specific references to certain novels and short stories, I found it interesting to watch the continuing evolution of Sherlock and John's friendship. I think it's great that the writers of Sherlock aren't holding back when it comes to the negative traits of Holmes's personality. We see the level of his selfishness as he takes off with Raz and allows John to be arrested. He also keeps John up all night when John starts his new job the next day. In typical Watson fashion, John manages to charm his boss by asking her out on a date. Of course, Sherlock crashes the date and doesn't seem to understand why John would want to romance Sarah when they should be working on the case. I'm wondering if Sarah is going to become the friend who has to take care of John's patients when there's a case -- assuming he hasn't been fired after their disastrous date!
I got a kick out of seeing another one of Holmes's contacts in the form of the graffiti artist. My first thought when I saw Raz was that he might be Wiggins of the Baker Street Irregulars. In a way, he serves the same function as the eyes and ears of London's street culture. He's able to track down the kind of spray paint that is being used in the ciphers, saving Sherlock some valuable time and energy. It was also cool to see Sherlock displaying his fighting skills. Unless I missed something, I don't think we ever learn the identity of the assailant that shows up at Baker Street. I wonder if he was someone Moriarty sent, or if this mystery assailant is like Kato in A Shot in the Dark and is someone Sherlock hired to keep his fighting skills sharp!
I'm sure there's much more I could say, but I'm getting hungry and people have probably fallen asleep. Besides, I should save some material for the next episode. *g*