Essential mathematical skills Book

I wouldn't necessarily say these stories feature rivals of Sherlock Holmes, as such. They are crime/mystery stories from roughly 1892-1906 or so; Russell asserts that "Most [...] were originally published while Sherlock Holmes was 'dead'" (i.e., 1893-1901).

I particularly liked "In the Fog" by Richard Harding Davis (3 stories), Arnold Bennett's "The Loot of Cities" (6 stories), and "The Hammerpond Mystery" by H.G. Wells.

My least favorite was the "The Mysteries of Great Cities" series by Baroness E. Orczy (there were 7 of them, and they quickly became predictable), but even that had an interesting premise initially, and the individual stories are quite short.