Thirteen-year-old Atticus "Tick" Higginbottom begins receiving mysterious letters from around the world signed only "M.G., " and the clues contained therein lead him on a journey to the perilous 13th Reality and a confrontation with evil Mistress Jane.
Twelve-year-old Seymour Hope and his ghostly "mother" Olive go to Scotland to claim a castle inherited from Ignatius Grumply's punster uncle, Ian, but while they tend an aged tortoise and face an unscrupulous developer, Iggie deals with Ian's ghost and aninept insurance agent.
In this story told mostly through letters, children's book author, I. B. Grumply, gets more than he bargained for when he rents a quiet place to write for the summer.