Andy and Terry's amazing treehouse has thirteen new levels. They've added a chocolate waterfall you can swim in, a volcano for toasting marshmallows, a bulldozer-battling level, a baby-dinosaur-petting zoo, a not-very-merry merry-go-round, a boxing elephant called the Trunkinator, an X-ray room, a disco with light-up dance floor, the world's scariest roller coaster and a top-secret thirty-ninth level which hasn't even been finished yet. But how can they enjoy all this brilliant stuff when they have to write a book faster they've ever done before? You'll have to read it to find out!