The Dark Ages in the Anglo-Saxon kingdom of Mercia, a time and a place where dragons and giants are held to be as real as eagles and wolves, where the old ways and the old gods have not been forgotten.
When a gravely wounded thegn arrives at the monastery by the mound on the hill, Dunstan the novice's world is turned on its head. Under the guidance of blind Ecgferth he must gather the plants known to cure and learn the charms to be sung if his wort-cunning is to save the man.
As the spear-companion Wulfgar slowly recovers, he tells Dunstan about the many strange creatures that inhabit this Earth. Together they search for a monstrous shape-shifting black dog known as the barghest, but since it can't be harmed by iron they must first find an ancient sword made in the days of Weland the Smith to slay it.