And so this week, more than 70 of them, many aged over 70 themselves, were on a pilgrimage to Meiringen in Switzerland, home of the Reichenbach Falls, and scene of the final struggle between Sherlock Holmes and his arch enemy, the evil Professor James Moriarty, often called "the Napoleon of crime".

Conan Doyle couldn't have chosen a more dramatic spot to stage the encounter. The falls plummet 250 metres down into the valley and such is the power of the water that it has created great holes and cavities in the rock.

And the spot where Holmes and Moriarty are supposed to have met - now handily marked with a little statue of the detective - is the most dramatic of all. The water plunges down a full 90 metres.

On their pilgrimage, members of the Sherlock Holmes Society are determined to add their own drama to the occasion. The society's president is Guy Marriott, a retired London lawyer, resplendent in the green dress uniform of the King of Bohemia.

"The King of Bohemia appears in an early short story called A Scandal in Bohemia. The king employs Sherlock Holmes to recover some compromising photographs of him with an opera singer."

We each choose the character we like to play, he says. "I like to dress up so a military uniform really is very suitable."

In fact, a love of dressing up is something all the Sherlock Holmes Society members clearly share, and since not everyone can be Holmes himself, or Watson, or Moriarty, even the most obscure characters are joining the pilgrimage.

Jonathan McCafferty, a former barrister, has chosen to be Cardinal Tosca. The Cardinal rates just one brief mention in just one Conan Doyle story, but Mr McCafferty sees this as an advantage.