The Deons opposed the Savants and their scientific methods. Meglos stole the Dodecahedron in the guise of the Fourth Doctor. Lexa, leader of the Deons, ordered his arrest. Zastor granted the real Doctor access to power room.
Lexa did not believe the Doctor's story about someone taking his appearance so she ordered a revolution. The Deons rose up and arrested the Savants. As non-believers they were sentenced to the surface. This was also Zastor's sentence. Lexa told him that his faith was but words without action. Lexa hoped that sacrificing the Doctor would return the Dodecahedron so they captured him and instigated a ceremony of his death.