When the Gray family moves from New York City to an old Connecticut house, nine-year-old Paul and seven-year-old Sue discover notes warning that the home is haunted. Their father is away on business, leaving Paul to act as man of the house, when strange things begin to happen. Mysterious footprints lead to a trap door beneath the barn, revealing a hidden cellar with a Revolutionary War-era bullet mould and a concealed spring. As the children investigate, they uncover a brand-new cigarette lighter with the initials C H, a mysterious gray feather inside Sue's locked room, and a shadowy figure lurking near the barn at night. A local boy named Ollie shares their interest in nature, but neighbors Barbara and Jerry insist the house truly is haunted. Paul devises a clever trap using Granny's flypaper and a bell to catch the prowler, but the shadowy visitor's motives remain unclear. With evidence mounting and secrets buried beneath the floorboards, the Gray children must decide whether they are facing a clever tramp or something far more unsettling in their new home.
