A City Sleeps follows Poe, the youngest member of The Silk, an ancient clan of dream exorcists that can enter the minds of sleeping hosts to rid their dreams of demons. When the residents of SanLo fall into an endless slumber, only Poe can rescue them from a never-ending nightmare. Equipped with her legendary Koto-sword "Heartstrings", and flanked by her stable of powerful ghost familiars, she must cleanse their dreams, and uncover the city’s dark secrets.