Osbert is 9 years old and the second son of Ealdorman Uhtred, Lord of Bebbanburg in Northumbria. Danes raid Bebbanburg and Ealdorman Uhtred's first son, also called Uhtred, is killed and his body desecrated after he is sent out to scout the raiders. Osbert is now the oldest son of Ealdorman Uhtred and is re-christened Uhtred.
Ealdorman Uhtred seeks to avenge his son's death, but is killed during the failed attack on Eoferwic (York) and Uhtred is captured by the Danish Earl, Ragnar the Fearless. Ragnar, intrigued and amused by the boy's attempted attack on him during the battle, retains him in his household as a thrall. Uhtred's uncle, Ælfric, takes Bebbanburg and the title of Ealdorman for himself, although Uhtred is the rightful heir.
