Finger, Finger!, by Harry Stephen Keeler (epub/Kindle/pdf)
If only Japan could lay her hands on the Thirteenth Coin of Confuscius, which was floating around somewhere in the United States, she could thwart a certain Chinese ambition. The Japanese Secret Service in New York had a clue and immediately a Japanese Secret Service Agent boarded the Chicago Flyer and never took his eyes of a white passenter with a short gray beard. It was the passenger's raincoat that the Secret Agent had his eyes on, and at the first opportunity he grabbed it and substituted a duplicate. Ina lightning fraction of a second, he shot his hand into the pocket. In the leather purse he found not the sacred gold piece but a dead finger wrapped in cellophane...
Thus the master mystery-man, Harry Stephen Keeler, lays the groundwork for one of his most fascinating stories in which he dramatizes the Oriental psychology of crime!