The White Ribband. Oathtakers, #1

Lost, alone, amnesiac; all that is left to him are a few tokens, and his name... Sir Gaheris cannot remember who his friends are, who he serves, or where he has come from. But he knows he must find his way back, whatever the cost. When he rescues Sir Medraut from certain death, the two swear an oath to help one another escape the enchanted woods that trap them, though it isn't only the strange forest that they must worry about... Something is hunting them. If they cannot escape, they will lose themselves-and each other-in the wandering woods.