In the land of Thra, a young guard discovers a terrible secret about the Skeksis overlords who control the planet -- and its powerful Crystal of Truth.

While Deet leads Rian on a harrowing journey through the tunnels of Thra, Seladon visits the Castle of the Crystal and sees a new side of the lords.

Desperate to save one of their own, the Skeksis make a deal with Aughra. Rian and Deet continue their search for the Dual Glaive.

As the Gelfling and the Skeksis prepare for a fateful battle, the Scientist starts work on a new secret weapon.