Victorian era pulp novel, 1890s vintage soft cover Nick Carter mystery w/ ads for cocaine etc

Worn 1890s antique pulp fiction, the famous Nick Carter in the story of The Great Enigma. You don't often see pulp paperbacks this old! Some great Victorian era ads inside.

This is missing the back cover, but I think perhaps the story is complete, it seems to match the rather abrupt style of the writing here.