'Imagine a horizon.' 'I can't.' Mithila's world is bound by a Wall enclosing the city of Sumer -- nobody goes out, nothing comes in. The days pass as they have for two thousand years: just enough to eat for just enough people, living by the rules. Within the city, everyone knows their place. But when Mithila tries to cross the Wall, every power in Sumer comes together to stop her. To break the rules is to risk all of civilization collapsing. But to follow them is to never know: who built the Wall? Why? And what would the world look like if it didn't exist? As Mithila and her friends search for the truth, they must risk losing their families, the ones they love, and even their lives. Is a world they can't imagine worth the only world they have? For fans of Isaac Asimov's Nightfall and Ursula Le Guin's The Dispossessed comes an astonishingly powerful voice in speculative fiction that explores what it means to truly be free.