On a quest in the Asian lands of Cathay, Prince Valiant encounters a fire-breathing mechanical dragon and the legendary adventurer Prester John. Armies converge, mountains crumble, and a father and son are reunited. Mordred escapes imprisonment and treacherously stabs Arn, who learns that Maeve is soon to give birth. Val discovers a lost colony and wrestles with a tusked whale off the coast of Greenland, but a spell overcomes the expedition on the Isle of Lost Youth.