Ranger's Apprentice the Royal Ranger 6:
Arazan's Wolves
John Flanagan

Will and Maddie are sent to neighbouring kingdom Celtica to investigate reports of terrifying direwolves - an ancient species thought to be extinct. What they discover is even more of a threat - a sorceress who has enslaved direwolves and Wargals to her will and is building an army of creatures both living and supernatural.