My Work Is Not Yet Done - Thomas Ligotti

When junior manager Frank Dominio is suddenly demoted and then fired, it seems there was more than a grain of truth to his persecution fantasies. But as he prepares to even the score with those responsible for his demise, he unwittingly finds an ally in a dark and malevolent force that grants him supernatural powers. Frank takes his revenge in the most ghastly ways imaginable—but there will be a terrible price to pay once his work is done. This tale of corporate horror and demonic retribution will strike a chord with anyone who has ever been disgruntled at work.