An author is meeting with the director of facilities of a retirement home. They know each other from when the director was a consultant for his previous book; he introduced the author to several residents who had tales of the Devil's Millhopper, a sinkhole in town.
The director has called the meeting because a resident died and left behind some unusual journals. The director figured it was right up the author's alley.
Everything about this is odd. The deceased resident, William James Henry, claimed to be one hundred and thirty-one years old. That's all we know about him because he never spoke, except to tell the caretakers his name and the year he was born: 1876.
The director is giving the thirteen journals (how prolific) to the author—temporarily, of course—in hopes that he can find out who William Henry was. However, he doesn't have very high hopes, because based on the brief selections he's read, they are most likely a work of fiction. Interesting.
Six months later (come on, the author is busy, folks), he finally sits down and reads the first three volumes from start to finish in one sitting. The story that follows is what those journals contained.