It's book week in Oakfield school and everyone is very excited. Including all the teachers, who are making costumes of their own. Mr Keen says there's an excellent prize on offer for best costumes worn on book day. So suddenly making a good costume is vitally important - but tricky. Delia's not much help (as usual) and the Fossils get carried away with the dressing up box. Marcus decides that he is a super hero and can't understand why 'Super Marcus' isn't the best name.