"There's still so much to do, but I feel differently these days. There are long roads ahead of us, but I'm not afraid."Kensho and Thurma
"And those long roads..."
"They'll wind into one another?"
"I'll move the worlds if need be. Remember, us Firelings are builders."
"And you and I?"
"We are two parts of something bigger."
The Glass Castle, home of the Firelings and their final protection, is under siege—and Thurma cannot defend it alone. But as her former rival, Nita, and the rest of her people come together, Thurma realizes that she has never been alone, and that working together is the only way to defeat The Fire That Stays.
In a flashback, Glasme emerges from beneath the rubble after the Fragor attack on her village. She finds her mother's remains shattered and realizes that The Fire That Stays has gone mad and that she must go to the Castle to stop him.
In Thra, Kensho finds himself stuck in the Prism. He is woken by Toolah, who has flown him away from the Branches. She tells him that he needs to stop doing things on his own and turn to his allies for help. Kensho decides that they have to allow the Branches into the Castle of the Crystal so that they may enter the Crystal Chamber. He tells the others that he plans to put himself between the Branches and the Crystal and must reach it before they do. Aiyana then reveals that she was born without wings and offers her synthetic wings to Kensho. The group flies to the Crystal Chamber on Bohrtog, where Toolah subdues the Royal Guard and the twins open the doors on Kensho's command. The Branches enter the Chamber as Kensho hovers in front of the Crystal.
In Mithra, Thurma, Nita and Fiola face The Fire That Stays and give him one last chance to surrender. He refuses and they attack, but he sends his wave at them. They conjure a wall to hold it back and struggle to maintain it, but the other Firelings join them, having been taught fire angling by Glasme.
In Thra, Kensho uses the power of the Crystal to absorb the Darkening and heal the Branches. He tells them that the Crystal's light belongs to them all and they must always work to balance it with the dark, which a clergyman admits to be wise words spoken by the true leader of the Gelfling. The crowd bows to a bewildered Kensho as Toolah, Dihnmor, Danevay and Aiyana watch in admiration.
In Mithra, Glasme joins the Ember Queens as the Firelings continue to repel The Fire That Stays' attack. Together, they build the Glass Castle, which repels his wave and sends it crashing down upon him, destroying him once and for all.
In both Thra and Mithra, the inhabitants celebrate their victory and survival. Aughra commends Kensho for creating a new beginning for the Gelfling, but tells him that he still has much to learn. Nita prepares to return home to aid the construction of glass tunnels to connect the homes of the Firelings while Fiola and Glasme rebuild the villages. As she and Thurma bid each other farewell, she reveals that she has named the Fragor hatchling "Camby", with whom Tumby is bonding. They agree that they will happily rule alongside Fiola and part ways.
Thurma examines a statue of her mother in the Great Hall. Kensho appears to her through the fire and comments that she seems kind, to which Thurma replies that she was. She asks him how things are in Thra and he tells her there is much to be done, but he is no longer afriad. He asks her if the long roads ahead of them will wind into each other and she tells him that she will move the worlds if need be. They recall what Cindrah told them, that they are parts of something bigger, always and forever, as they share a kiss.