Oscar is blamed for a crescendo of naughtinesses, which he claims are all done by his friend, Billy. Only, no-one can see Billy. This would be the ususal story about an imaginary friend, except there is a twist at the end. There really is a Billy, and a right little horror he is too. Tony Ross's adults are sharp-nosed and unsympathetic, while Oscar is round and cuddly. The author is very much on the side of the child, even though the havoc created is truly horrendous.