A Conspiracy in the Underground Fortress (Chiteijou no Inbou- 地底城の陰謀)

Duke Zaki came from Boazan to visit Prince Heinell. He harassed Heinell of his failure so far to conquer the Earth and also of his background of being a son of the traitor named La Gour. The Duke then made a plan to kill Heinell in a fight with Voltes by forcing Heinell to pilot the beast fighter Gargo. But Zaki's plan was shattered to pieces as Kazarin eavesdropped the plan and leaked it to Prince Heinell.