Off Season is a novel written by Jack Ketchum. It was first published in 1980.
September. A beautiful New York editor retreats to a lonely cabin on a hill in the quiet Maine beach town of Dead River—off season—awaiting her sister and friends. Nearby, a savage human family with a taste for flesh lurks in the darkening woods, watching, waiting for the moon to rise and night to fall...
And before too many hours pass, five civilized, sophisticated people and one tired old country sheriff will learn just how primitive we all are beneath the surface...and that there are no limits at all to the will to survive.