After two fan-pleasing episodes, Sherlock brings Season 3 to a close with His Last Vow. A case of stolen letters leads Sherlock Holmes (Benedict Cumberbatch) into a long conflict with Charles Augustus Magnussen (Lars Mikkelsen), the Napoleon of blackmail, and the one man he truly hates. But how do you tackle a foe who knows the personal weakness of every person of importance in the Western world? BBC One has also released a behind-the-scenes featurette with the cast and crew sharing their thoughts on Sherlock's best man speech, how things will change for Sherlock and John, and the chemistry between Martin Freeman and Amanda Abbington. His Last Vow debuts this Sunday, January 12 on BBC One before making its stateside premiere February 2.