The Flame Bearer (The Saxon Stories #10) by Bernard Cornwell

Britain is at an uneasy peace. After their bloody defeat of Danish-held East Anglia, the West Saxons stand victorious while the Mercians have taken back their land on the border of Northumbria, the last kingdom of Britain still ruled by the pagan northmen. A precarious truce exists between Æthelflæd’s Mercia and Northumbria, now ruled by Uhtred of Bebbanburg’s son-in-law, Sigtryggr.