A young American boy — he never gives his name, but his Norse companions call him Able — falls through a gap between worlds and finds himself in Mythgarthr, a realm modeled on Norse and Arthurian mythology where seven levels of reality are stacked vertically, from the divine Kleos at the top to the icy underworld of Nifl at the bottom. Able is given the gift of a knight's body by a magical being called a Mossmaiden, but his mind remains that of a boy — a child in a warrior's frame, trying to understand what it means to earn the identity he has been handed. The novel is narrated in retrospect as a long letter Able writes to his brother back home, a device that establishes an unreliable, selective narrator uncertain about his own truthfulness. Gene Wolfe builds a secondary world of rigorous internal consistency, drawing on medieval chivalric codes, Norse cosmology, and Arthurian romance, while the real subject is the gap between who a person is and who they are becoming — and whether heroism can be willed into being or only discovered.