Septimus is on the threshold of his fourteenth birthday, which falls on the shortest day of the year. While everyone celebrates and the Castle is lit with the traditional candles, Septimus has greater concerns on his mind. He has finally reached the period in his Apprenticeship known as Darke Week. During this crucial time, he hopes to undertake the very dangerous mission of restoring Alther from Banishment, following the attempted invasion of the Castle of Syren. But while this preoccupies him, other Darke things are afoot in the Castle.