The Saga of Aslak Slave-Born

Harken!
This is the saga of Aslak Ottarssen, born a slave.
Aslak, and his beloved sister, Astrid, are the children of a Norwegian farmer. Their mother was an English slave.
Their father chooses to free Aslak. But Astrid remains a slave.
Aslak promises that he will buy her freedom when he is a man and can earn enough silver. At fifteen, he goes viking to earn his fortune.
Returning from sea, he finds that his father has died. Worse: his step-brothers have sold his sister.
Furious, Aslak leaves his home forever, and calls on his ship-brothers to help him find and free his sister.
He pursues Astrid across the North: a violent and dangerous place in the Viking Age. His hot temper leads to him being sold into slavery himself, in Jorvik, capital of England's Danelaw.
But, captive among strangers, he finds unexpected help, faces death, sees a ghost - and meets still more danger.
Can Aslak regain his own freedom and rescue his lost sister?