Blackveil. Book Four

Karigan G'ladheon was a regular girl until she stumbled across a dying man. There were two arrows embedded in his back, and wherever his horse was taking him, he was going to die before they got there. He gave Karigan his horse, his cloak and his brooch - the symbol that he was one of the King's Green Riders - and, with them, his mission. To deliver a message to the King. He made her swear to do it ...
even though the Shadow Man who killed him would be hot on her trail. That mission made her a Green Rider. Now, her first legendary mission is long complete. Karigan has learnt to wield the magic her Green Rider brooch allows her to access, and she's used it to defy some of the most terrifying dark magicians of the age. But while Mornhavon the Black has gone, he's not defeated. His restless spirit haunts Blackveil, the lethal, corrupt forest that stands beyond a failing magical wall at the edge of King Zachary's territory.
Karigan's destiny is leading her there, and when her King asks her to join a mission to Blackveil to save the remnants of a dying race, it seems she has little choice but to follow it ...