Martin Fartingale hates English weather, hates Cornwall and most of all, hates his name. He is staying with his mother and batty grandmother in a small fishing village over looking St. Cecils Mount, an intriguing rocky blob at the end of a causeway out to sea. Ignoring the warnings of  his new school friends Danny and Charlotte (Charlie) that no-one has ever escaped from St. Cecils Mount, Mart5in decides to break into the ancient building and explore. He finds himself face to face with Gregor, the Mad Monk, Ursula, a black witch – and he must defeat Sir Bullimore Fergus in sword fighting and the Black Knight in a joust, with unexpected allies the ghost of Uncle Septimus Fartingale (who appears as a foul-smelling green vapour) and a white witch who looks remarkably like Charlie.