Dragonsbane (Winterlands, Book 1)

Highly successful stand-alone novel by the author of the bestselling Darwath Trilogy.
It was said to be impossible to slay a dragon. But Lord John Aversin had earned himself the name of Dragonsbane once in his life and had become the subject of ballad and legend. Fired by the romance of his tale, young Gareth travelled far and wide across the Winterlands from the King’s court to persuade the hero to rid the Deep of Ylferdun of the great Black Dragon, Morkeleb. With them on their quest went Jenny Waynest, half-taught mage and mother of Aversin’s sons.
Although the most fearsome dragon that Aversin had ever faced, Morkeleb was not the greatest danger awaiting him and his witch-woman. The once-ordered court had fallen into decadence and dissolution, and the beautiful sorceress Zyerne held the King in her sway. Just as Morkeleb posed the greatest challenge for Dragonsbane, so Jenny Waynest would find her powers pitted against an adversary as deadly as the Black Dragon – and infinitely more evil.