The Once and Future King Book 1, Chapter 11

The boys are told that fairies cannot stand iron, so as long as they hold small iron knives, they can walk into the castle and retrieve the captives, walking out again, as long as they don't eat any of the fairies' enchanted food. The boys are sent with Marian through the dark, wild forest. At first they resent being with a woman, but soon they find that she is a great warrior. The fairies sense the iron knives the boys carry, and turn their castle into food, to tempt the boys to eat. A drawbridge made of butter, however, is not very appetizing, and the boys simply walk in, confront Morgan with their iron, and leave with the prisoners. But a giant Griffin has been guarding the castle-a creature that is part falcon, part lion and part snake-and Morgan releases it to attack Robin and his crew. Just as Arthur is about to be killed by the Griffin, Kay shoots an arrow through its eye and kills it. They all go to sleep, because it is too late to return home, and in the morning, Kay brings the Griffin's head home with him with great pride.