This is more about Sherlock's deadly drug addiction than anything else. His brother Mycroft (one of my favorite characters) and Watson conspire to get him help by luring him to Venice, where Sigmund Freud is. Yes, Freud is in fact a main character. I love that! He's played by Alan Arkin.
While the drug issue is the main plot, there is a mystery to be solved. It's a Sherlock movie, so there has to be. It is drug-related, however, but I won't give it away.
The main issue here is the casting. Robert Duvall is miscast as Dr. Watson, and although I think the man playing Sherlock, Nicol Williamson, is a good actor, he isn't Sherlock. He's still likable, however, so I can't complain about him too much. Vanessa Redgrave and Laurence Olivier are also in this, and Charles Grey, the actor who played Mycroft in the Jeremy Brett series, plays him in this as well, which came before that series. He's not in it long enough, though!
Fair warning: the story may take awhile to pick up for some people, but it does. There is a fun train chase scene nearer the end. It makes for a good climax.
As far as Sherlock movies go, it isn't brilliant, but I liked it.
My grade: B