Halt's Peril by John Flanagan
While chasing the leader of the Outsiders cult, Halt is ambushed and shot by a poison arrow. Not realizing that Halt has been poisoned, he, Will and Horace continued their chase. But soon, the effect of the poison is evident and Will sees that Halt is slowly dying. The only person that can help Halt is the sorcerer, Malkallam. Will quickly sets out to find him, but will they be fast enough to save Halt from death?
Will stepped clear of the tree, pivoting so that he emerged on the opposite side. And his mouth went dry as he saw the assassin aiming a crossbow toward Halt, heard the dull smack of the cord. Halt had warned him that they might have more than one bow apiece and he'd been right.
Then Will's heart froze at the most chilling sound he had heard in his young life: Halt's brief cry of pain, followed by the sound of his bow dropping.
**Book 9 in Ranger's Apprentice**
Previous book: The Kings of Clonmel
Next book: The Emperor of Nihon-Ja