Martha is bored with her dog, cat and goldfish. So off she goes to the pet shop to buy a monster. But the monster she chooses has an appetite unequaled in children's literature. He soon proves to be rather a handful as he eats his way through all the wood in Martha's house leaving her knickers draw-less and her bed leg-less! In a bid to rid herself of this fearsome green pest she takes him back to the pet shop where she is told that she can't have her money back. It is exchange only - and Martha looks set to do it again by choosing a very unusual egg!