Green Knowe is a place whose past haunts its present. Mrs. Oldknow relates to the 2 boys an incident out of Green Knowe's past, when the mysterious Dr. Vogel took up residence at Green Knowe as the family tutor in the year 1630. Dr. Vogel became caught up in some nefarious activity, and as the boys soon learn, the evil force that was unleashed by Dr. Vogel still lurks in the present day. They must confront this challenge to Green Knowe and its proprietor in a series of hair-raising events