Feeling trapped inside his house, Mr Benn heads off to the costume shop for an adventure. After the shopkeeper gives him a blue uniform and hat, Mr Benn wonders what he will be; stepping through the changing room door he finds himself at a zoo, and realises that he must be the zookeeper. However, all the animals in this zoo are sad and unhappy. A parrot explains that the animals are miserable because their cages are too small - so Mr Benn decides to turn the tables on the zoo’s visitors, by showing them what it is like to be locked up…