On the eve of World War I, 21-year-old Georgie Hyde-Lees meets the acclaimed poet W. B. Yeats at a soirée in London. Although Yeats is famously eccentric and many years her senior, Georgie is drawn to him, and when he extends a cryptic invitation to a secret society, her life is forever changed. As Georgie finds purpose tending to injured soldiers in a makeshift hospital, she befriends the wounded and heartbroken Lieutenant Pike, who might need more from her than she is able to give. At night, she escapes with Yeats into a darker world, becoming immersed in the Order, a clandestine society of ritual and magic. As forces --- both of this world and the next --- pull Yeats and Georgie closer together and then apart, Georgie uncovers a secret that threatens to undo it all.