Hannah and Eric Rosenthal are devout Jews living in North London with their three children and Eric’s father Yosef, a Holocaust survivor. Both intellectually gifted and deeply unconventional, the Rosenthals believe in the literal truth of the Old Testament and in the presence of God (and evil) in daily life. As Hannah prepares to publish an account of Yosef's years in war-torn Europe—unearthing a terrible secret from his time in the camps—Elsie, her perfect daughter, starts to come undone. And then, in the wake of Yosef’s death, she disappears. When she returns, just as mysteriously as she left, she is altered in disturbing ways.

Witnessing the complete transformation of her daughter, Hannah begins to suspect that Elsie has delved too deep into the labyrinths of Jewish mysticism and gotten lost among shadows. But for Elsie’s brother Tovyah, the truth is much simpler: his sister is the product of a dysfunctional family, obsessed with rituals, traditions, and unbridled ambition. But who is right? Is religion the cure for the disease or the disease itself? And how can they stop the darkness from engulfing Elsie completely?