In episode two Sherlock, Season 4, Sherlock faces perhaps the most chilling enemy of his long career: the powerful and seemingly unassailable Culverton Smith, a man with a very dark secret indeed. "The Lying Detective" is written by Steven Moffat. Benedict Cumberbatch returns as Sherlock Holmes, with Martin Freeman as John Watson, Mark Gatiss as Mycroft Holmes, Rupert Graves as Inspector Lestrade