Since her stepmother's recent death, 17-year-old Briony Larkin knows that if she can keep two secrets—that she is a witch and that she is responsible for the accident that left Rose, her identical twin, mentally compromised—and remember to hate herself always, no other harm will befall her family in their Swampsea parsonage at the beginning of the twentieth century. The arrival of Mr. Clayborne, a city engineer, and his university-dropout son, Eldric, makes Briony's task difficult. Clayborne's plan to drain the swamp has made the Old Ones unhappy, particularly the Boggy Mun, who has plagued the village's children with swamp cough in retaliation. When Rose's lingering illness turns into a cough, Briony knows that she must do whatever it takes, even revealing her secrets, to save her sister. While thwarting the advances of an arsenic-addicted suitor, Briony must also deny her feelings for Eldric, even as he helps her solve the puzzle that has become her life.
She is never cold, she always knows exactly what time it is, and her hair grows two inches while she sleeps. Fifteen-year-old Corinna Stonewall--the only Folk Keeper in the city of Rhysbridge — sits hour after hour with the Folk in the dark, chilly cellar, "drawing off their anger as a lightning rod draws off lightning." The Folk are the fierce, wet-mouthed, cave-dwelling gremlins who sour milk, rot cabbage, and make farm animals sick. Still, they are no match for the steely, hard-hearted, vengeful orphan Corinna who prides herself in her job of feeding, distracting, and otherwise pacifying these furious, ravenous creatures. The Folk Keeper has power and independence, and that's the way she likes it.