To clarify:
'I have seen scandal within the Czech Republic'
Wilhelm Gottsreich Sigismond von Ormstein, the King of Bohemia (part of what is now the Czech Republic), engages the services of Holmes in the short story 'A Scandal in Bohemia'.
'a blue jewel' refers to the missing item in The Adventure of the Blue Carbuncle (a carbuncle being a type of jewel).
'six French leaders' refers to another short story 'The Adventure of the Six Napoleons'.
Originally posted by Roger007Yes, that was the clue that eluded me the longest. For some reason I had it in my head that the leaders were literal people. In the story, some seeming madman is going around shattering wax busts of Napolean. He had hid a black pearl in one of them to avoid a police search, and was keen on recovering the prize.
'six French leaders' refers to another short story 'The Adventure of the Six Napoleons'.