Charlie Braithwaite is at home in his bedroom. It is a boring, wet afternoon, when suddenly, his old friend the archwizard Argetlám appears on his computer screen. At first delighted by the return of his friend, he soon discovers that the wizard has a job for him that is both extremely dangerous and possibly, crucially important to the freedom of everyone living in modern Britain. Argetlám explains to Charlie that Athelwan, an evil sorcerer punished for his wicked ways by entombment in a cavern, centuries earlier, has escaped. Furthermore, he has materialised during the Battle of Britain, in 1940s England. The sorcerer has taken the job of headmaster of the local school and Argetlám is convinced that he is trying to help Britain's sworn enemy, the evil Nazis. Should he succeed in his scheme, Britain may well lose the battle and therefore, her freedom. The consequences of this re-writing of history being that even people as young as Charlie could be seriously affected, perhaps not even born. Our hero is therefore persuaded to travel back to September 1940, in the guise of a London evacuee. Once there, he is to enrol at Athelwan's school, where the sorcerer has taken the name Benson, in order to spy on him.