Fifty years after the death of Dr Watson (Blakely), a safety deposit box containing his private papers is finally unlocked. Amongst the deerstalking caps, pipes and hypodermic syringes lies an unpublished account of the real Sherlock Holmes (Stephens) and the one case that he didn't manage to solve successfully.
Galvanised into action when a mysterious Belgian woman arrives on their doorstep after taking an unwelcome dip in the River Thames, Holmes and Watson find themselves embroiled in a case that involves everything from the Loch Ness monster to circus midgets, a group of Trappist monks and Queen Victoria.
Unlike the rest of Wilder's work, "The Private Life of Sherlock Holmes" has always been somewhat underrated.
That's partly because the studio savaged the original three hour cut of the film - arbitrarily snipping out two additional cases that Holmes and Watson investigated - to get the movie down to its present two hour running time.
As a result of this butchery, Wilder's attempts to turn Holmes into a tragic figure - whose retreat into the life of the mind is simply a response to painful affairs of the heart - is lost in the reshuffle.
Fortunately, the script is brilliant enough to work even in this reduced form - with the captivating performances of Stephens and Blakely putting a hilariously camp spin on Wilder's overblown adventure.
There is some fantastic support from the redoubtable Irene Handl ("Did you ever try doing embroidery with a gun in your hand?") and Christopher Lee as Sherlock's brother, Mycroft.
While it never achieves what the lost three hour print could have accomplished, this is still one of the sparkiest adventures that the private detective ever left 221b Baker Street for.
The Private Life of Sherlock Holmes (1970)
