Twelve-year-old Cecily Lockwood and her older brother, Jem, leave their father behind in war-torn London and travel with their socialite mother to the country estate of Uncle Peregrine. Arriving at the village, Cecily discovers other children being evacuated, most of them alone and frightened, waiting to be chosen by strangers to board with them. Cecily wants one for herself, to bring home to the manor with them. After her mother surprisingly agrees, Cecily chooses a girl named May. Although May comes from a poorer background, she is clever and unwilling to be controlled by Cecily, who wonders if perhaps she has made a poor choice. In the meantime, fourteen-year-old Jem is straining to do something for the war effort and is at odds with his mother, while their uncle plays host, shaded by his own dark mystery. The discovery of the ruins of Snow Castle by May and Cecily prompts Uncle Peregrine to tell a story, a true tale of royalty and betrayal and of sons and mothers and murderous uncles, one that reaches across the centuries and into their present life. May and Cecily also discover two strange boys at the ruins, brothers whose story comes to life as the days pass.