The Witch's Brat — Rosemary Sutcliff

The Abbey of New Minster means safety to Lovel. It is the reign of Henry I in England, and the monks protect Lovel from the people who think that, because of his crooked back and healing skills, he must be a witch. And, he has nowhere else to go. Then he meets Rahere, the King's Jester, in the abbey - and makes a bargain that will take Lovel to London, to establish a life of his own at the great hospital of St Bartholomew.