"The Devil Within" is a novelette that introduces readers to some of the characters in Madeleine Holly-Rosings "Boston Metaphysical Society" comic series.
In this outing, we meet Andrew O'Sullivan, who is a medium and a spirit photographer: he's able to take pictures of ghosts at crime scenes, as well as seeing them when they visit his home. Andrew is not one of the well-to-do; we see his genteel poverty throughout the story.
This story concerns the dual murders of a servant couple in the home of one of Boston's Upper Crust.
Holly-Rosings' alternate history Boston is an entertaining, if challenging (things aren't pretty there), world to visit. This little book is a great introduction.