To save her seven-year-old daughter, a single mother must confront a sentient fungal entity that has invaded their lives in this chilling new novel from the acclaimed author of The River at Night and Girl in Ice.

In the rainy suburbs of Boston, where humidity lingers and fungal blooms thrive in every damp corner, scientist and single mother Dani Walters notices a disturbing change in her young daughter after the girl eats wild mushrooms from their backyard. Once sweet and affectionate, she has become sullen and secretive, claiming to hear a voice that demands she do terrible things?but when Dani confronts her, she blames an imaginary friend.

As her daughter's behavior grows more frightening, Dani searches desperately for an explanation, fearing the early onset of a psychological disorder that runs in their family. Or, as Dani's father insists, is it something darker?something evil?

As a fungal eruption engulfs the basement of their home, spreading with an intelligence and purpose that defies everything Dani knows about the natural world, the bond between mother and daughter will face its most terrifying test.

A nightmare of ecological and psychological horror, this dark and unforgettable novel asks: What if the person you most love became the very thing you most fear?