Question

Justify the title A SHADY PLOT

Answer 1

AS the author used to take help from a ghost to the title is quite right. As the word shady is used for dark which in this case is a ghost and plot is a trap or scheme, which the narrator used by making a plan of getting help from the ghost 

Answer 2

A shady plot refers to a storyline which is full of mystery, supernatural elements, murder, ghosts etc. The given story is about the ghost of Helen who has human qualities. It is a shady story which has mysterious and uncanny occurrences. So the title is appropriate.

Hallock did not get the plot of the story on his own. He got it from  someone else. The things which occurred with Hallock formed the plot of his story. He got all this because of the arrival of the ghost. So as the plot is got from someone else, it is a shady plot.