One King's Way is the second part of the trilogy by Harry Harrison and John Holm (Tom Shippey) that began with The Hammer and the Cross.
[1][2][3][4] Shef is now co-king of a realm in southern Britain.
After getting separated from his comrades in a sea battle with the Ragnarssons, he begins an epic journey through Scandinavia.
Also travelling through Scandinavia is Bruno, a Christian knight in search of the Holy Lance, hoping to restore the empire of Charlemagne.
The book was followed by the final part of the trilogy, King and Emperor.