Miss Mephistopheles by Fergus Hume

When Kilsip undertook to educate Naball in the business of a detective, he gave him an epigrammatical piece of advice: "Cultivate curiosity. " This golden rule Naball constantly followed, and found it of infinite service to him in his difficult profession. He was always on the lookout for queer cases, and when he discovered one that piqued his curiosity, he never rested until he found out all about it. The Red Indian follows the trail of his enemy by noting the most trivial signs, which to others with a less highly cultivated instinct would appear worthless. And Naball was a social Red Indian, following up the trail of a mystery by a constant attention to surrounding events. A casual observation, a fleeting expression, a scrap of paper -- these were the sign-posts which led him to a satisfactory conclusion, and he never neglected any opportunity of exercising his faculties.

By this constant practice he sharpened his senses in a wonderful degree, and cultivated to the highest extent the unerring instinct which he possessed in discovering crimes.