Years ago, the Voltron Force ultimately defeated Prince Lotor, resulting in his horrible disfigurement and Voltron being retired. But before Lotor was captured, he sent Castle Doom away to an unknown location. Now in the present, Keith, Allura, Amalgamus and a supposedly reformed King Zarkon are trying to learn from Lotor where Castle Doom went. Meanwhile, space pirates have reemerged and begun attacking Alliance ships and colonies.