Sentence:  ... I discovered this particular one to be merely a shallow recess in the limestone, nowhere reëntrant to a distance of over forty feet, of the general proportions of a tin oven, and transacting an immense business of mystery (or what they call, as far west as this, ""Shenandigan"" and "<WSD>"Scullduggery</WSD>"") with those who gape at it from below, on the capital of a dark, overgrown portal, as big as the cave itself. 
Meaning of the word marked with <WSD> tags:  Dishonest, underhanded, or unscrupulous activities or behaviour.