Riven is a protector, and her world is one of sharp steel, quiet forests, and the unshakeable reality of her duty. Her life is governed by the practical, the predictable, and the presence of the Arborheart—a colossal, dead tree that has stood dormant for centuries.

But when the Arborheart explodes with a surge of impossible, chaotic life, Riven's world is fractured. The tree's explosive growth reshapes the landscape and unleashes a volatile magic that is as wondrous as it is deadly.

Her only guide through the chaos is Soren, a disgraced scholar whose heretical theories about the living land have just become terrifyingly real. As a ruthless, technologically advanced kingdom arrives to claim the tree's power for its own, Riven and Soren are forced into a desperate alliance. They must unravel the Arborheart's secrets before its magic is twisted into a world-ending weapon, or worse, before the strange magical sickness it has unleashed consumes everyone she has sworn to protect.

The greatest secret, however, may not be the one hidden in the heart of the tree, but the one the Arborheart has awakened in Riven herself.