One of the classics of the fantasy genre. It opens with the first-person narrator recounting how Holger Carlsen, a Dane, had come to America for education and worked for the same company as the narrator -- until World War II, when he went back to Denmark to work for the resistance. Except that at one point, trying to cover an escape, pinned down by Nazi forces, he suffers a head wound and wakes up to find himself in an old growth forest. With hawks. And a bear. He could believe the others, but there were no bears left in Denmark.
Happening on a witch who summons what she calls a sprite -- involving reciting the Lord's Prayer backwards -- helps murk things up more. She is told that he comes from far, far, far away, and sends him off with a dwarf, Hugi, toward the local elf hill and Duke Alfric, who may help clear up things. At Hugi's suggestion, he first meets with a swan may, Alianora and she comes with them, filling him in the relations between Law and the lands of men, and the tricksy, uncertain fairy forces of Chaos, which are threatening to engulf the world and end day.
The story wends on, though the complications of discovering who Holger really is, and the peril of the world, and it involves a unicorn, a magician who rashly advertises ever-filled purses, an attempt to persuade Holger to get out of the way, unhurt, and a discovery that he knows how to fight as a knight, a knight in shining armor who collapses entirely, proving to be an empty suit of armor, when defeated, detecting which person is a werewolf, a nixie without a soul, a riddle game, and much more.
(Anyone who plays D&D and recognizes things is right about the recognition. D&D had to find its notions somewhere.)