The Thousandth Woman by E.W. Hornung

Hilton Toye was the kind of American who knew London as well as most Londoners, and some other capitals a good deal better than their respective citizens of corresponding intelligence. His travels were mysteriously but enviably interwoven with business; he had an air of enjoying himself, and at the same time making money to pay for his enjoyment, wherever he went. His hotel days were much the same all over Europe: many appointments, but abundant leisure. As, however, he never spoke about his own affairs unless they were also those of the listener -- and not always then -- half his acquaintances had no idea how he made his money, and the other half wondered how he spent his time. Of his mere interests, which were many, Toye made no such secret; but it was quite impossible to deduce a main industry from the by-products of his level-headed versatility.

Criminology, for example, was an obvious by-product; it was no morbid taste in Hilton Toye, but a scientific hobby that appealed to his mental subtlety. And subtle he was, yet with strange simplicities; grave and dignified, yet addicted to the expressive phraseology of his less enlightened countrymen; naturally sincere, and yet always capable of some ingenuous duplicity.