After telling his class about the ghost of Captain Kidd and his buried treasure on George’s Island, George is placed in a foster home. George and another foster child, Bonnie, flee to the island on Halloween but when they’re followed by adults Captain Kidd’s ghost is awakened.

The queen of an unnamed European country is being pressured by her Prime Minister to abdicate the throne in favour of one of her sons. But she wrestles with the question which son, the older but emotionally unstable Prince Calvin or the younger but more mature Prince George, will be named as her successor. Meanwhile, a series of murders of the palace staff is being committed by an unidentified “Skulker”, whom the queen begins to suspect may in fact be one of the princes.