Grace is woken in the middle of the night to the sound of an armoured horse in her back garden. The next thing she knows, a dying Grace doppelganger bursts through her bedroom door and insists that she is the fifteenth and final Grace, and it is her destiny to win the Worthy War. Grace's quest takes her to the county of Brokenshire, where she must work with her trusty steed (who has a sharp tongue and a habit of reminding Grace of all the ghastly ends her predecessors have met!) to battle magical creatures and save the world.

A vegan T. rex, a distinguished dodo, bomber geese and the fearsome trigger wolf are amongst the cast of memorable characters Grace meets on her adventure.