 The book brings together three strangers -- John, Jack and Charles -- in London during World War I, where they become entrusted with the Imaginarium Geographica, an atlas of all the lands that have ever existed in myth and legend, fable and fairy tale. They end up traveling to the Archipelago of Dreams, fighting the dark forces that threaten two worlds. It is later revealed that the three are future fantasy authors J.R.R. Tolkien, C.S. Lewis and Charles Williams, who met in real life at Oxford and enjoyed a competitive friendship.