Okay, guys! So my life has finally stopped spontaneously combusting and I finished reading A Study in Scarlet. I'm going to try to wrangle my thoughts into submission on the subject.

There are a lot of similarities between the two stories, but I hadn't realized all of the differences yet. Obviously they cut out the Mormonism subplot, because it's not really considered in good taste these days. I think it's clever how they managed it, because it's an issue that has kept the story from getting adapted frequently.

In taking that out they had to vastly change the murderer's motives--although they keep the same dichotomy between vengeance and love ("bitterness is a paralytic. Love is a much more vicious motivator.") The murders in the episode are a bit less focused than the murders in the story, as the cab driver is merely killing people to get money for his children, not going after specific people he wants to get revenge on.

Otherwise, the adaptation sticks pretty close. I think it's kind of sad that they had to change the story so that the cabbie (who actually IS listed in the credits as Jeff Hope, fun fact) is divorced from his wife. In the novel he had a really beautiful love story with Lucy, even if they were never able to be together, and it's a shame that it couldn't be salvaged. Still, it's a good solid adaptation, and pretty cleverly done.

I like the little nods to the original story. The coffee cups that John and Mike Stamford drink out of say "Criterion" because Watson and Stamford originally dined at the Criterion restaurant in the novel. The scene in which Sherlock beats the corpse with the riding crop is a reference to something Stamford says he has seen Sherlock doing in the laboratory as a test. The "Rache" clue left behind is twisted on its ear--in the novel it is German for revenge. Sherlock warns them "don't bother for looking for Miss Rachel." The clue also turns out the be a red herring. In the episode Sherlock suggests that the writing is meant to say "Rachel." When questioned about it, he responds "No, she was leaving an angry note in German. Of course she was writing Rachel!" And this piece of information turns out to be an important clue to solving the case. Also, the American in the back of the taxi that Sherlock chases down is a reference to the fact that in the book the victims are Americans.

All in all, I think it's a clever and inventive adaptation.