The Adventure of Charles Augustus Milverton

Sherlock Holmes is hired for another case. The target this time is a professional blackmailer who buys compromising letters of people and then presses them for loads of money. Lady Brackwell turns to Holmes with the hope of him finding and getting rid of old letters to a younger boy. Holmes and Watson try to blend into the blackmailer Milverton's home. And when they finally get themselves to Milverton's safe, they get involved in a murder.
This was not the initial plan. What happened? Who was the victim and who was the murderer? Find out the end in "The Adventure of Charles Augustus Milverton".