In Mr. Holmes has Holmes with an unsolved case 50 years ago to fight an aged Sherlock.
Sherlock Holmes is 93 years old and has itself in Sussex to rest. He has left behind the Baker Street and his faithful partner Dr. Watson is also no longer on the side of the former master detective. Age has left its mark and its comprehension and observational skills that even were they no longer are. But a case that it is now 50 years back, can be Sherlock Holmes no rest, and so he is, to put together the puzzle.