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.
Continuing their efforts in the ever-expanding treehouse, Andy and Terry tackle the mystery of their missing publisher, Mr. Bignose, whose disappearance has made completing their next book rather difficult.
Andy and Terry try to meet a latest book deadline despite distractions in their sophisticated tree house home, including flying cats, giant bananas, and sea monsters pretending to be mermaids.