Sir Arthur Conan Doyle , The valley of fear.

The first half of this novel is pretty standard Sherlock stuff, the second half however, strays from Doyle's usual mechanisms . Irish America, reds, the American coal fields, pinkertons.  Solid pulp, a little boring at the outset but it builds up throughout.

 http://www.gutenberg.org/ebooks/3289
   several free versions here