Ranger's Apprentice: The Royal Ranger - Arzans Wolves #6 - By 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.