Sword Song was Rosemary Sutcliff‘s last children’s book, left in manuscript form on her desk when she died in 1992. In summary, the story is this:
Sixteen year old Bjarni Sigurdson, a young Viking swordsman, did not mean to kill the holy man who had kicked his dog but the horse-pond was near and Bjarni did not think the old man would drown in the short time he held him under. But he did and Bjarni was guilty of man-slaying. To make matters worse hid Chief, Rafn, had sworn an oath that in his settlement the followers of Christ should be safe, so Bjarni had made his chief an oath-breaker.
Bjarni is given a sword and banished from the settlement for five years. He becomes a mercenary, making a life for himself as a swordsman. He journeys from England to Dublin, and then to the islands off the west coast of Scotland where he finds a hero in a Viking seafarer. He proves himself in five years of adventure, fighting among the clan chiefs from the west coast of Scotland in bitter, bloody feuds; seafights are interspersed with the domesticity of harvests and weddings.
At last Bjarni’s five years are up and he decides to return to his own settlement. But there are more dangers in store for him. He is shipwrecked and becomes involved with a girl who is in danger of being killed because she is thought to be a witch.