Seventeen-year-old Sarah is a Sensor, gifted with the ability to survive within the sentient Ecosystem that swept away human civilization centuries ago. While the remnants of humankind huddle in small villages of stone, Sarah uses her psychic connection to the Ecosystem to travel freely in the wild in search of food, water, and fuel. Sarah doesn't fear the Ecosystem—but she hates it for killing her mother when Sarah was a child. When she hunts, she hunts not only for her people's sustenance but for revenge.

Then Miriam, an apprentice Sensor, is lost in the Ecosystem, and Sarah sets out to rescue her. Joining Sarah is Miriam's beloved, Isaac, a boy who claims to possess knowledge of the Ecosystem that will help their people survive. The harrowing journey to find the missing apprentice takes Sarah and Isaac into the Ecosystem's deadliest places. And it takes Sarah into the unexplored territory of her own heart, where she discovers feelings that threaten to tear her—and her society—apart.

A thrilling fantasy adventure from the author of Freefall and the Survival Colony series, Ecosystem is the first book in an epic cycle that includes The Devouring Land (2018), House of Earth, House of Stone (2019), and The Last Sensor (2020).