In the desert city of Alabaster, an ancient Tower has kept seventy thousand people alive for centuries — and Taryn has always been able to hear something in its hum that no one else can. When he's tested and revealed as the first Commander in five hundred years, he inherits a city with a failing aquifer, a dormant protective dome, and an army on its way. The machines have been waiting for someone who could finally listen.

A year after unlocking a door sealed for five centuries, fourteen-year-old Taryn is learning that open doors invite everything in — including a rogue ancient intelligence quietly resuming an unauthorized mission and a band of outcasts with legitimate grievances marching toward the coast. None of it is catastrophic on its own. Together, it's a different story. Taryn built something open and good; now he has to find out if those two things can survive each other.

At sixteen, Taryn commands a planetary network, carries the legacy of the colony's founder, and is the only person who can hear the ancient machines well enough for what comes next — because two ships have entered the system, and every colony they've found before is gone. With three weeks to prepare forty-seven thousand people, he discovers the terraforming program has been quietly reshaping the planet for the ships' passengers all along, and the founder's sealed plan can't be opened until it's almost too late. Taryn has operators, allies, and an AI that's been waiting two centuries for this moment — and one final decision that has nothing to do with the ships, and everything to do with what it cost to build something worth saving.