Merlyn instructs Arthur and his brother Sir Kay in the ways of the world. One of them will need it-- the king has died leaving no heir, and a rightful one must be found by pulling a sword from an anvil resting on a stone. In the second and third parts of the novel, Arthur has become king and the kingdom is threatened from the north. In the final two books, the ageing king faces his greatest challenge, when his own son threatens to overthrow him. In The Book of Merlyn, Arthur's tutor Merlyn reappears, and teaches him that, even in the face of apparent ruin, there is hope.