Three Hearts and Three Lions

This novel is Poul Anderson at his swash-buckling best. He is bawdy and funny and the action is fast. Holger Carlsen was an orphan who was raised in Denmark, leading a fairly normal life, until the Nazi machine stepped forward. Then while on a mission for the underground resistance Holger disappears and is "translated" into another world, one where magic, dragons, witches and trolls are all real. Holger is without memory of this land, but his body does remember and through his many adventures, he comes to realize that he is an important cog in the battle between chaos and law, in two separate, yet oddly similar worlds.