I saw this film a number of years ago and loved. When I found it on Netflix, I rented it and loved it all over again. Michael Caine and Ben Kingsley play beautifully off each other, the comedy is both subtle and broad, and the atmosphere of late Victorian London is painstakingly recreated. It bombed upon its release, but has been rediscovered as a comic gem.
The basic premise: John Watson is actually the brilliant, crime-solving detective who's had to hire a very thick drunken actor to play Sherlock Holmes. Couldn't find a trailer, but here is a scene near the beginning of the film.
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