Arthur, High King of Britain by Michael Morpurgo - old paperback
As the sea sweeps in, the boy is suddenly cut off in his attempt to walk round the Scilly Isles from Great Ganilly to St Martin's. Having given up hope of survival, he finds himself waking up beside a warm fire with the man, Arthur Pendragon, and his dog, Bercelet, who have rescued him. Arthur tells him the incredible story of his life while the seawater dries out of boy's clothes. His tale begins with his legendary pulling of the sword from the stone, his leadership of an army to defeat the Saxons and his celebrated court at Camelot. From then on, he tells of the great and tragic love between himself, Guinevere and Lancelot and the numerous deeds and adventures of the knights of the Round Table. Finally, the curse of Morgana Le Fey come true and Arthur's son, Mordred, kills him, but not before he can watch Bedivere return Excalibur to the Lady of the Lake. After the wonders of the story, the boy returns home, looking forward to surprising his family with his adventure - but time in the cave where Arthur hibernates until it is time for him to rule again has stood still, and the boy's family have not even noticed he was gone.