Sherlock resumes his hunt for Moriarty when Sebastian Moran reveals that a man who was thought to be dead from a heart attack was actually on the list of intended victims from Moriarty. Vinnie Jones returns as the sinister "M." F. Murray Abraham guest stars as "The Actuary," a devious hitman.
Sherlock agrees to take a case from a man claiming to be Moriarty, hoping it will bring him closer to finding his nemesis. Meanwhile, Gregson encourages Joan to give up the dangerous line of work she has chosen and go back to being a sober companion. Natalie Dormer guest stars as Irene Adler.
When a hedge fund manager who was also running a Ponzi scheme is murdered, Holmes and Watson must determine which of his clients is guilty. Also, Sherlock contemplates sponsoring a fellow recovering addict.
Holmes and Watson join forces with the NYPD after a police officer is murdered. Also, Sherlock searches for the creator of a "recovery blog" who is posting personal statements he has made in sobriety meetings.
In the series finale, the POI Team – Finch, Reese, Fusco and Shaw – embark on one final mission to prevent Samaritan from destroying The Machine and cementing its hold over mankind.
