Stephen King "The Ten O'clock People"

The main character, who is a smoker trying hard to quit for health reasons, discovers a horrible aspect of reality that only those attempting to quit like him are capable of seeing - that many of the people living among us in positions of power, including many police and political figures and even the Vice President, are in fact inhuman monsters disguised as people. A unique chemical balance, caused by his smoking only on his morning break (thus the reference to Ten O' Clock in the title) makes him able to see the true nature of these creatures through their disguises.
Ten O'Clock People is a short story by Stephen King published in the Nightmares and Dreamscapes collection. Unlike many of King's stories which take place in fictional places like Castle Rock, Maine, "Ten O'Clock People" takes place in the distinctly recognizable Boston, Massachusetts.