The Evening and the Morning by Ken Follett

England, in the year 997. Edgar is a young boatbuilder who barely escapes death when the Vikings raid his harbor town.
His family loses all that they have and migrates further inland, to scratch out a living farming in a town dominated by a lazy ferryman and a corrupt priest.
Normandy, the same year. Ragna is a smart, headstrong, beautiful noblewoman. She could marry the wealthy French baron chosen for her by her doting parents, but chooses instead a dashing Englishman nobleman, Wilwulf, who visits her father to seek a treaty that will protect the English coast from the Vikings.
Ragna finds friends, enemies and danger in her new life in England.