The TV series, set in the late 9th and early 10th centuries, follows the adventures and misadventures of Uhtred of Bebbanburg, a Saxon noble boy who is captured by Danes and raised as one of them. After the death of his adopted Danish family, he finds himself torn between his Danish and Saxon heritages, but eventually swears his sword to King Alfred of Wessex, a pious and godly king who believes it is his destiny to unite the seven Saxon kingdoms together as one: England. Alfred and Uhtred have a complex relationship, with Uhtred saving Alfred's life on several occasions but Alfred struggling to create a Christian kingdom when his greatest warrior refuses to convert to the cross.
The TV series is based on The Saxon Stories, a series of novels by historical fictional writer Bernard Cornwell. The series is planned to expand across 14 novels (eleven of which have been published), which in total will follow Uhtred and the fate of Wessex from Alfred becoming King in 871 all the way to the Battle of Brunanburh in 937, when the fate of England is finally decided; Uhtred will presumably be in his eighties in the last novel of the series. The series is loosely based on real history, with the caveat that the historical Uhtred actually lived a century after the fictional one.