Thorstein is the youngest son of a Norse family settled at Greenodd. Up-country is wild and unknown, but Thorstein is driven north by destiny, where he discovers the lake now called Thurstonmere. He is cheated out of his inheritance, and nearly out of his true love, but all comes well at the end. The book climaxes with a siege on Peel Island by the Saxons which he withstands. He dies valiantly, as befits a Viking, in a glorious defeat. His children and their descendants settle at Nibthwaite.