The mood and diction of the story is supposed to be suspenseful eerie like their is something coming you can't see
This the mood and diction of the story not scary but scary in the sense that the sickness is lying in every corner
There was no light of any kind emanating from lamp or candle within the suite of chambers. But in the corridors that followed the suite, there stood, opposite to each window, a heavy tripod, bearing of fire, that projected its rays through the tinted glass and so glaringly illumined the room.
I think this is symbolism in the sense that the missing of "light" means their is evil or evil arriving that they can not see coming
So I picked a tree for the theme here is why so they try to hide in the castle that is represented by the leaves up high but roots represent the illness so my thoughts i got from the story was no matter how high of power or low of power you can hide from it run from it but destiny will fulfill its self.