Many have read James Chaney's book William the Baptist, published in 1877. I didn't realize until last night (thank you, R. Andrew Myers!) that he wrote a sequel in 1894: Agnes, the Daughter of William the Baptist - or, The Young Theologian. It's written in a similar style to William the Baptist, combining narrative and dialogue, and looks like a great read.
Franklin Pierce Ramsay evidently was both a BCO nerd and a storyteller. He wrote A Exposition of The Form of Government and the Rules of Discipline of the Presbyterian Church in the United States, and a novel: The Question. No, I haven't read the novel, so I have no idea if it's any good. But the mere fact that a 19th-20th century Presbyterian pastor and teacher wrote a novel is a bit startling. Check it out and let us know what you think.