Hirm - L. Ron Hubbard

Professor James Lowry didn't believe in ghosts, witches, or demons. That is, until one beautiful spring evening, when his cloak went missing and he suddenly couldn't remember the last four hours of his life. The quiet college town of Antwothy now begins to change, slowly at first, but then with each attempt by Lowry to remember, things start to change faster and more terrifyingly. Lowry is pursued by mysterious dark forces that turn the world against him, while whispering a warning from the darkness: "If you find your cloak, you will find these four hours. If you find your four hours, you will die."