In this episode, long-buried secrets catch up with the Baker Street duo. Someone has been playing a long game indeed and Sherlock and Watson face their greatest ever challenge. Is the game finally over?

Benedict Cumberbatch returns as Sherlock Holmes, with Martin Freeman as John Watson, Mark Gatiss as Mycroft Holmes, Rupert Graves as Inspector Lestrade, Una Stubbs as Mrs Hudson, Amanda Abbington as Mary Watson, Louise Brealey as Molly Hooper. Season 4 of SHERLOCK on MASTERPIECE concludes with “The Final Problem” on Sunday, January 15, at the special time of 6PM on KTWU-HD, Digital Channel 11.1.