On a gusty March day in 1016, Earl Uhtred of Northumbria, the most powerful lord in northern England, arrived at a place called Wiheal, probably near Tadcaster in Yorkshire. Uhtred had come with forty men to submit formally to King Canute, an act that completed the Danish subjugation of England and the defeat of Ethelred the Unready, to whom Uhtred had been a loyal ally and subject. But, as Richard Fletcher recounts in the electrifying opening to...