The Three Impostors. by Arthur Machen

Two idlers in London are sauntering in the streets when they pick up a coin dropped by a fleeing man. They keep meeting three persons, each time in a different disguise, who recount lurid tales. They seem to be looking for a spectacled man who regrets working with them, and has run away with a valuable coin ... This novel is a Gothic horror classic, and takes the form of an episodic novel, with each chapter containing a story recounted by one of the three impostors.
It contains "Novel of the Black Seal" and "Novel of the White Powder, " popular stories which have been widely anthologized.