Ever tried to get out of going to school by pretending that you're dead? Ever managed to convince a friend that they're invisible? Ever been stuck in a gorilla suit and nearly put in a zoo? Andy has. Andy's the greatest practical joker in the world ... well, almost. He would be, if only his practical jokes didn't have the annoying habit of backfiring on him.

Andy and Terry have a new book to write, but there's a problem. A BIG problem. Well, quite a few big problems actually.... On a hill not too far away there is a tree. And in that tree there is a tree house. And in that tree house there is a bowling alley, a see-through swimming pool, a tank full of sharks, a giant rope swing, a library full of comics, a secret underground laboratory, a vegetable vaporiser and a free marshmallow-dispensing machine.

On a trip to Principal Greenbeard's office, Henry McThrottle discovers that there is buried treasure on Skull Island, which is somewhere in the school! Henry and his friends Jenny, Gretel, Newton and Jack set out to find a chest filled with gold, jewel-encrusted goblets and pieces of eight (whatever they are). But soon their secret is out, and everyone has treasure fever. Can they find the buried treasure, beat the bully, catch the villain and save their teacher, Mr Brainfright?

Andy and Terry have built their biggest and most astonishing treehouse yet! It has everything they – and you – could wish for, including an electric pony stable, a Santa Land, a NOISY level, a kangaroo-riding range, a WHATEVER-WEATHER-YOU-WANT dome, a 100% edible gingerbread house and a hall of funhouse mirrors. But Anti-Andy, Terrible-Terry and Junkyard-Jill, their doppelgangers, are trapped in one of the mirrors – and they want out.

Can Zack save the earth from butts gone berserk? Can he defeat the biggest, ugliest, meanest butt the world has ever seen? More importantly, will Zack and his butt ever find true happiness? It's an adventure you and your butt will never forget!