Sherlock takes a case from a man that claims he is Moriarty, in the hope that it will bring him closer to finding his nemesis. Meanwhile, Gregson suggests to Joan to give up the line of work she has chosen and go back to being a sober companion.

As Sherlock reels at the reappearance of his former lover, Irene Adler, a series of flashbacks unravel the tumultuous events that led to his downfall into addiction.

Sherlock Holmes, who is still recovering from his gunshot wound and is taking painkillers, deals with a case of currency manipulation and murder in a Greek shipping company. It comes to a showdown between him and Moriarty.

Holmes and Watson come face-to-face with Moriarty when their adversary is brought in as a consultant on a kidnapping case. Meanwhile, Detective Bell continues his struggle on the road to recovery.

Together on Graham's sofa: singing superstar Cher and actor Christine Baranski, starring in movie sequel 'Mamma Mia! Here We Go Again', brilliant actor and writer Rupert Everett, promoting his new film about Oscar Wilde, 'The Happy Prince', and 'Game of Thrones' star Natalie Dormer starring in BBC drama 'Picnic at Hanging Rock'. With music from Tom Odell, performing his new single 'If You Wanna Love Somebody'.