Like Poe himself, the author sets the mood of the story with a locked room mystery tone or mood.  Sis is somehow taken out of the locked room while Edmund is out buying food. Immediately, the reader is confronted with the task of figuring out how Sis was taken from the room when the door remained locked.  In addition to this effect, other elements such as:

"Fog plays an important role in events, hiding or disguising figures who move about dark streets and across the city's piers."

And how the story itself is written contributes to the mood or tone of the work.

"Organizing The Man Who Was Poe as if it were a drama gives the novel a strong you-are-there tone, with characters and clues standing out in high relief from scene to scene, making the settings and people easy to visualize."