The Diva's Ruby by F. Marion Crawford

When Van Torp and Logotheti left Mr. Pinney's shop, the old jeweller meant to have a good look at the ruby the Greek had brought him, and was going to weigh it, not merely as a matter of business, for he weighed every stone that passed through his hands from crown diamonds to sparks, but with genuine curiosity, because in a long experience he had not seen very many rubies of such a size, which were also of such fine quality, and he wondered where this one had been found.

Just then, however, two well-dressed young men entered the shop and came up to him. He had never seen either of them before, but their looks inspired him with confidence; and when they spoke, their tone was that of English gentlemen, which all other Englishmen find it practically impossible to imitate, and which had been extremely familiar to Mr. Pinney from his youth. Though he was the great jeweller himself, the wealthy descendant of five of his name in succession, and much better off than half his customers, he was alone in his shop that morning.