A case of stolen letters leads Sherlock Holmes into conflict with Charles Augustus Magnussen.

His Last Vow will be broadcast next Sunday at 8:30pm on BBC One. The episode stars Benedict Cumberbatch  as Sherlock Holmes, with Martin Freeman as John Watson, Mark Gatiss as Mycroft, Rupert Graves as Inspector Lestrade, Una Stubbs as Mrs Hudson, Amanda Abbington as Mary Morstan, Louise Brealey as Molly Hooper and Lars Mikkelsen as Charles Augustus Magnussen. The episode is written by Steven Moffat.