Sherlock: His Last Vow

This episode (the last of season 3) has Sherlock pit against Charles Augustus Magnussen, a man who holds secrets on all kinds of powerful people. This is where we learn that Mary has a very violent, secret past. I do not believe the Mary of the books ever had such a past. The TV movie is very similar to the story in this case. This man is really, extremely, evil. In the book Sherlock allows him to be murdered without interfering. On the TV episode, he murders him himself. All of the secrets die with him onscreen; in the short story, Sherlock burns all the papers.