The four main characters were mice living at Oxford Circus Underground station. They use the Tube to get around London, taking them to wherever their latest adventure was supposed to take place.
The mice had their own society, using rubbish thrown away by humans (the mice had a strict code prohibiting theft). They had their own compartments on Underground trains and decorated their tunnels with reused junk. This society included mouse businessmen, mouse underground supervisors and even mouse Members of Parliament.
