Eduardo Lucas was a society gentleman and amateur tenor living in London. He was also secretly a spy for an unnamed foreign country, and is referred to by Sherlock Holmes as one of the three top spies in the city. Holmes realises him to be one of the key players during "The Adventure of the Second Stain", but he is murdered before Holmes has the change to interview him. It is later revealed that he lived a second life in Paris as "Monsieur Henri Fournaye", and that his wife murdered him because she believed he had been unfaithful. However, as she has gone insane, she is of no use as a witness either.