A haunting, heartbreaking post-apocalyptic tale of female friendship and intimacy.'A small miracle' The New York Times‘For a very long time, the days went by, each just like the day before, then I began to think, and everything changed’Deep underground, thirty-nine women live imprisoned in a cage. Watched over by guards, the women have no memory of how they got there, no notion of time, and only vague recollection of their lives before. As the burn of electric light merges day into night and numberless years pass, a young girl - the fortieth prisoner - sits alone and outcast in the corner. Soon she will show herself to be the key to the others' escape and survival in the strange world that awaits them above ground.WITH A NEW INTRODUCTION BY SOPHIE MACKINTOSH, MAN BOOKER PRIZE-LONGLISTED AUTHOR OF THE WATER CURE